Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

The geology and petrology of the Averill Alkaline Plutonic Complex, near Grand Forks, British Columbia Keep, Myra 1989

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1989_A6_7 K37.pdf [ 10.17MB ]
Metadata
JSON: 831-1.0052531.json
JSON-LD: 831-1.0052531-ld.json
RDF/XML (Pretty): 831-1.0052531-rdf.xml
RDF/JSON: 831-1.0052531-rdf.json
Turtle: 831-1.0052531-turtle.txt
N-Triples: 831-1.0052531-rdf-ntriples.txt
Original Record: 831-1.0052531-source.json
Full Text
831-1.0052531-fulltext.txt
Citation
831-1.0052531.ris

Full Text

THE GEOLOGY AND PETROLOGY OF THE AVERILL ALKALINE PLUTONIC COMPLEX, NEAR GRAND FORKS, BRITISH COLUMBIA. By MYRAKEEP B.Sc, The University of London, England, 1987 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS OF THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF GEOLOGICAL SCIENCES We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April 1989. o Myra Keep, 1989. In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of b£OU3<aiG\U S06r4C£S The University of British Columbia Vancouver, Canada Date 3c5tk iUaxJ DE-6 (2/88) i i ABSTRACT The Averiil Alkali Plutonic Complex is an informal name given to a suite of alkalic plutonic rocks that occur in southern British Columbia, approximately 80 kilometres north of Grand Forks. The suite comprises five plutonic members, ranging in composition from pyroxenite to syenite, which have been intruded by two later coeval dyke swarms. The first four members of the plutonic suite include pyroxenite, monzogabbro, monzodiorite and monzonite, and define a concentrically zoned intrusion with pyroxenite at the centre and monzonite at the edge. The fifth member, a syenite, was intruded through the centre of this concentric zonation, causing brecciation of the pyroxenite and monzogabbro. The first four members of the alkali suite have the same mineralogy, including pyroxene, amphibole, biotite, alkali feldspar, plagioclase feldspar, apatite, sphene, oxides and sulphides, with occasional epidote. The only difference between the four lithologies is the modal proportions of each mineral present. The syenite differs in mineralogy comprising essentially alkali feldspar with interstitial mafic phases and poikilitic garnet. Apatite and sphene are also present. Electron microprobe analysis demonstrates that the constituent pyroxenes are uniformally augite/salite, and some zoning is present. The amphibole is hornblende, that shows no variation in chemical composition. Biotite has a uniform composition also. Poikilitic garnet in the syenite is andraditic in composition. Alkali feldspars in the pyroxenites to monzonites range from orthoclase (100) to albite (100). Plagioclase compositions range from albite (100) to anorthite (50). The syenites contain only alkali feldspar ranging from orthoclase 70 to orthoclase 100. There is good field, petrographic and geochemical data to propose that the pyroxenite to monzonite sequence of rocks is cogenetic. Furthermore, Pearce element ratio diagrams suggest that the syenite can be related to the monzonite through simple fractionation of alkali feldspar. Rare platinum group element mineralization in the map area is associated with copper rich mineralization derived from the intrusion of the syenite. i v TABLE OF CONTENTS ABSTRACT ii TABLE OF CONTENTS iv LIST OF TABLES vii LIST OF FIGURES viii LIST OF PLATES x ACKNOWLEDGEMENTS xi INTRODUCTION 1 1. GEOLOGY 2 1.1. LOCATION AND ACCESS 2 1.2. PREVIOUS WORK 2 1.3. REGIONAL GEOLOGY 3 1.4. LOCAL GEOLOGY 5 2. PETROGRAPHY 13 2.1. ALKALINE ROCK SERIES 15 2.1.1. Pyroxenite 15 2.1.1.1. Field Occurrence and Petrography 15 2.1.2. Monzogabbro 17 2.1.2.1. Field Occurrence and Petrography 17 2.1.3. Monzodiorite 17 2.1.3.7. Field Occurrence and Petrography 17 2.1.4. Monzonite 18 2.1.4.1. Field Occurrence and Petrography 18 2.1.5. Syenite 18 2.7.5.7. Field Occurrence and Petrography 18 2.2. DYKES 21 2.2.1. Trachyte 21 V 2.2.1.1. Field Occurrence and Petrography 21 2.2.2. Porphyry 23 2.2.2.1. Field Occurrence and Petrography 23 2.3. SUMMARY 23 3. MINERAL CHEMISTRY 29 3.1. ELECTRON MICROPROBE ANALYSIS 29 3.1.1. Operating Conditions 29 3.1.2. Analytical Conditions 31 3.1.3. Detection limits, analytical accuracy and precision 38 3.2. CHAIN SILICATES 38 3.2.1. Pyroxene 39 3.2.2. Amphibole 39 3.3. GARNET 41 3.4. BIOTITE 41 3.5. FELDSPAR 41 3.5.1. Alkali Feldspar Series 45 3.5.1.1. Units 1 to 4 45 3.5.1.2. Unit 5 45 3.5.2. Plagioclase Series 45 3.6. ACCESSORY MINERALS 46 3.6.1. Apatite 46 3.6.2. Sphene 46 4. GEOCHEMISTRY 47 4.1. MAJOR ELEMENTS 47 4.1.1. Major and minor element distribution 47 4.1.2. Chemical Trends 49 vi 4.1.3. Differentiation Processes 54 4.1.3.1. Units 1 to 4 54 4.1.3.2. Unit 5 59 4.1.3.3. Unit 6 66 4.2. TRACE ELEMENTS 66 4.2.1. Trace element distribution 66 4.2.2. Discrimination diagrams 70 4.3. CONCLUSIONS 70 5. PETROGENESIS 73 5.1. FIELD EVIDENCE 73 5.2. CHEMICAL VARIATION 73 5.3. SUMMARY 77 6. IGNEOUS PROCESSES AND PLATINUM MINERALIZATION 79 6.1. FIELD EVIDENCE 79 6.2. GEOCHEMICAL EVIDENCE 79 6.3. COMPARISON TO OTHER Pt BEARING BODIES 81 6.4. CONCLUSIONS 85 7. CONCLUSIONS 86 REFERENCES 88 APPENDIX A - REPRESENTATIVE ELECTRON MICROPROBE ANALYSES 93 APPENDIX B - REPRESENTATIVE WHOLE ROCK CHEMICAL ANALYSES 106 APPENDIX C - GEOCHRONOLOGY 110 v i i LIST OF TABLES Table 2.1 - Table showing the mineral occurrences in each rock 14 Table 3.1 - Electron microprobe operating conditions 30 Table 3.2 - Electron microprobe analytical conditions for pyroxene and garnet 32 Table 3.3 - Electron microprobe analytical conditions for biotite and amphibole 33 Table 3.4 - Electron microprobe analytical conditions for feldspar 34 Table 3.5 - Electron microprobe analytical conditions for apatite 35 Table 3.6 - Electron microprobe analytical conditions for sphene 36 Table 3.7 - Chemical analyses in atomic per cent of all of EMP standards 37 Table 4.1 - Whole rock chemical analyses 55 v i i i LIST OF FIGURES Figure 1.1- Schematic map of British Columbia showing Cordilleran tectonic provinces and map area 04 Figure 1.2 - Schematic stratigraphic column showing the relative ages of rocks at the Franklin Camp 06 Figure 1.3 - Geologic map of the Averill alkali plutonic complex 07 Figure 1.4 - Cross sections across the Averill alkali complex 09 Figure 2.1 - Schematic diagram showing concentric pluton 25 Figure 2.2 - Geology of the westernmost structurally controlled outlier 27 Figure 2.3 - Geology of the easternmost structurally controlled outlier 28 Figure 3.1 - Pyroxene quadrilateral diagrams showing pyroxene composition 40 Figure 3.2 - Feldspar composition shown on Ab-An-Or triangles 42 Figure 4.1 - Harker diagrams showing whole rock major element chemical variation with respect to S i02 for the Averill suite 48 Figure 4.2 - Alkalis vs. silica diagram showing the alkaline affinity of the rocks of the Averill suite 50 Figure 4.3 - AFM diagram showing the chemical affinity and differentiation trend of the Averill complex 51 Figure 4.4 - AFM diagram showing comparison of Averill data to that of the Kruger syenite, southern B.C. 52 Figure 4.5 - AFM diagram comparing the Averill suite with Thingmuli volcano 53 Figure 4.6 - Pearce element ratio diagram to model feldspar separation, using P as a conserved element 60 Figure 4.7 - Pearce element ratio diagram to model feldspar separation using P as a conserved element 61 Figure 4.8 - Pearce element ratio diagram to model the effect of alkali feldspar using P as a conserved element 62 Figure 4.9 - Pearce element ratio diagram to model the effect of Al in feldspar, using P as a conserved element 64 Figure 4.10 - Pearce element ratio diagram to model the effects of ferro-magnesian minerals on differentiation 65 i x Figure 4.11 - Harker diagrams showing the variation in trace elements with respect to silica 67 Figure 4.12- Diagram to show the relative enrichment of Sr with respect to Rb 69 Figure 4.13- Trace element tectonic discrimination diagram. 71 Figure 5.1 - Inferred cross-sections with contacts based on contact relationships seen on the surface 74 Figure 6.1 - Distribution of soil geochemical platinum/palladium anomalies with respect to soil copper anomalies 80 Figure 6.2 - Comparison of the Averill plutonic complex with the Tulameen ultramafic complex in Southern B.C. 82 Figure 6.3 - Comparison of the Averill plutonic complex with the Lac des lies ophiolite in Quebec 83 Figure 6.4 - Comparison of the Averill plutonic complex with the Sudbury structure in Ontario 84 Figure A. 1. - Sample location map 109 Figure A.2. -1:5000 geologic map of the Averill alkaline plutonic complex -insert X LIST OF PLATES Plate 1 - Brecciation of monzogabbro by syenite intrusions 11 Plate 2 - Photomicrograph of pyroxenite showing augite phenocrysts with opaques and apatite 16 Plate 3 - Photomicrograph of augite zoning in monzodiorite 19 Plate 4 - Photomicrograph of monzonite showing remnant augite grains, plagioclase, alkali feldspar and quartz 20 Plate 5 - Photomicrograph of poikilitic garnet in syenite 22 Plate 6 - Photomicrograph to show weathered, altered grains within Unit 7. 24 xi ACKNOWLEDGEMENTS I would like to thank Placer-Dome Inc. for suggesting this thesis topic, and for providing field and logistical support during the summer of 1987. Funding for this project was from the British Columbia Department of Energy, Mines and Petroleum Resources Mineral Development Agreement, the Natural Sciences and Engineering Research Council of Canada operating grant A0820 awarded to Dr. J . K. Russell, and from Graduate Teaching and Research Assistantships awarded to the author. I also acknowledge Dr. J . K Russell for supervising this research and critically reviewing the manuscript many times before the final draft. I would also like to thank Drs. R. L. Armstrong, J . V. Ross and H. J . Greenwood for reviewing the manuscript. My thanks are gratefully extended to the following people who provided assistance with many aspects of my thesis: Maggie Piranian and John Knight (electron microprobe); Stanya Horsky (X-ray florescence); Urs Mader, Umakanth Thirugnanam, Kelly Russell and Cliff Stanley (data reduction); Bryon Cranston and Mark Baker (crises management); Yvonne Douma (thin sections); Dita Runkle (geochronology); and Dave and Diane Onions (food, shelter and hot water). Therapeutic fun during the preparation of this thesis was provided by the Geology Grad Group and the Geology Womens Hockey Team, while therapeutic whining sessions were chaired by Michelle Lamberson, Steve Sibbick and Jan Hammack. Therapeutic R and R was provided by Pamela Keep, who had the foresight to fly her daughter home for Christmas, and finally, therapeutic extra curricular activities were provided by Slug, who also provided much of the chocolate consumed during the last 2 years, as well as working the pump of the ego-inflator. 1 INTRODUCTION Compared to their calc-alkaline counterparts, alkaline rocks are relatively scarce. In part, the paucity has limited the study of their mineralogy, chemistry and petrogenesis. Alkaline rocks host a number of rare minerals and are important for tectonic interpretation as well as for their economic mineral potential (Mutschler et al., 1985). Although alkaline rocks in British Columbia have been known for some time (Drysdale, 1915; Little, 1957), they have recently been the focus of renewed research (Keep and Russell, 1988). This is mainly due to the discovery of new alkaline-hosted precious metal deposits (Rebagliati, 1989). However, there still remains a lack of quantitative data on mineral and whole rock chemistry. This thesis presents new, comprehensive data for the Averill alkaline plutonic complex, Grand Forks, British Columbia. Mineralogy and chemistry constrain the petrogenesis of these intrusions, thereby allowing insight into the igneous processes that are involved in the creation of alkaline rock suites. Petrology may be used to infer the tectonic setting of these suites. 2 1. GEOLOGY 1.1. LOCATION AND A C C E S S The "Averill Alkaline Plutonic Complex" lies in the Franklin mining camp, approximately 65 km north of Grand Forks, British Columbia, near the confluence of Franklin and Burrell Creeks at the base of Mt. Franklin (NTS 82E/9W). The plutonic complex is on the northwest side of the mountain. The area is reached by travelling north along the North Fork Road from Grand Forks to the Burrell Creek forestry road at 48 km. At 25 km along the Burrell Creek road there is a service road which leads to the Union Mine at the base of Mt. Franklin. A number of tracks around the mountain allow access for four-wheel drive vehicles. 1.2. PREVIOUS WORK The Franklin Camp area has been actively explored since the 1900's. The Union Mine, which exploited a gold-copper bearing quartz vein, was established on the property in 1912 and was active until 1935. The earliest geologic mapping was conducted in 1911 (Drysdale, 1915). More recently an exploration program was initiated by Franklin Mines Ltd (Lisle and Chilcott, 1965), and in 1968 the Newmont Mining Corporation of Canada conducted a regional program in the area (Norman, 1969). The Union Mine property is currently held by Sumac Ventures Inc., which conducted surface and underground drilling in 1985 and 1986, and established a leach plant on the property in 1987. The most recent activity includes exploration and drilling conducted by Placer-Dome Inc., in 1987 (Pinsent and Cannon, 1988). 3 1.3. REGIONAL GEOLOGY The Franklin mining camp is situated in the central Monashee Mountains at the southern end of the Omineca Crystalline Belt (Figure 1.1). The Omineca is the eastern metamorphic core zone of the Cordilleran Orogen (Parrish et al., 1988), and in southern British Columbia comprises basement gneisses; deformed and metamorphosed rocks of the North American continental margin sequence; allochthonous rocks of the Intermontane Superterrane; and Palaeozoic, Middle Jurassic, Upper Cretaceous and Paleogene granitic rocks, deformed under compression during the Mesozoic. All were overprinted by Cenozoic crustal extension (Parrish et al., 1988). The southern Omineca Crystalline Belt comprises broadly divided into two types of tectonic elements (Ewing, 1981; Armstrong, 1982; Price, 1981,1985; Price et al., 1985; Parrish and Carr, 1986; Parrish et al., 1988). These are:-1) upper Proterozoic to Jurassic rocks of low to moderate metamorphic grade. The late Paleozoic and mid-Jurassic are overlain in part by Eocene strata (such as that found at Franklin camp) and are juxtaposed on major faults against and above rocks of the second tectonic element, which is 2) high grade metamorphic crustal rocks with a strong Cretaceous and lower Tertiary overprint. The major faults that juxtapose these two elements are regionally extensive low- to moderate-angle normal faults of Eocene age (Bally et al., 1966; Monger et al., 1982; Parrish et al., 1988; Parrish et al., 1988). In southern British Columbia these faults include the Valkyr shear zone and the Greenwood-Granby, Slocan Lake, Kettle, Okanagan, Columbia River and Purcell Trench faults. Most of the easterly dipping fault systems were active 58 to 52 million years ago, and the westerly dipping faults were active 52 to 45 million years ago (Parrish et al., 1988). The Granby-Greenwood fault near 4 Rgure 1.1- Schematic map of British Columttashc^ tectonic provinces and map area. 5 Grand Forks is one of a group of faults that falls along the trend of the east side of the Republic graben in northern Washington and is the one that most directly affects the Franklin mining camp (Little, 1957; Pearson and Obradovich, 1977). An Eocene period of magmatic intrusion (45 to 60 million years ago) has been recognized in the southern Omineca belt (Armstrong, 1988; Baadsgaard et al., 1961; Miller and Engels, 1975). This magmatism is known as variously the Rocky Mountain orogeny (Baadsgaard et al., 1961), the Cordilleran orogeny (Burchfiel and Davis, 1975), or simply as Eocene plutonism and magmatism (Cheney, 1980; Griffiths, 1977). This period of plutonism and magmatism resulted in late phases of the Nelson batholith and a number of alkaline plutons comprising the Coryell batholith were emplaced at this time (Baadsgaard et al., 1961). The Coryell batholith is by far the most voluminous of the Eocene intrusions, and its plutons are exposed over approximately 100 k m 2 in the Monashee Range of mountains, centred near Grand Forks, British Columbia, as shown in Figure 1.2 (Leroux, 1980; Little, 1957, 1961,1963; Parrish et al., 1988; Daly, 1912). 1.4. LOCAL GEOLOGY The oldest rocks outcropping in the Franklin Camp are Permo-Carboniferous Franklin Group sediments and volcanics that have undergone multiple deformation and intense thermal metamorphism (Drysdale, 1915; Pinsent and Cannon, 1988). Many of the units are difficult to distinguish as they grade between hornfelsed tuff and tuffite (Pinsent and Cannon, 1988). The Franklin Group rocks have been intruded by granitic plutons of mainly Mesozoic age (Little, 1957) which are themselves cut by rock of the Averill alkaline plutonic complex, which is Jurassic in age (Appendix C). The age relations of all of the lithologies local to the Franklin camp are portrayed schematically in Figure 1.2. 6 GLACIAL TILL MARRON VOLCANICS KETTLE RIVER FM. AVERILL PLUTONIC COMPLEX JURASSIC GRANITES FRANKUN GRP SfKrtSn S t r a t i 9 r a P h i c « l u m n showing the relative ages of rocks at 118^23' 49'35 'H h 49*34' figure 1.3 - Geologic map of the Averill alkali plutonic complex (as mapped by author) reduced in size from Enclosure 1 (back pocket). 8 Figure 1.3 is a reduced size geologic map of the Averill alkaline complex, showing the distribution of the various lithologies. The original 1:5000 geologic map showing actual outcrop distribution may be found in the map pocket at the back of the thesis (Enclosure 1). The Averill alkaline complex comprises a northwest-southeast trending series of ultramafic and alkaline rocks which have a concentric zonation grading from clinopyroxenite at the centre, through monzogabbro and monzodiorite, to monzonite at the edge. Boundaries between these four lithologies are distinguished on the basis of the colour index of the rock. Intruding though the pyroxenites to monzonites along the same trend is a body of augite syenite. Forceful intrusion of the syenite through the pyroxenite/monzogabbro has resulted in brecciation of the latter (Plate 1). Xenoliths of pyroxenite /monzogabbro in the syenite range in size from approximately 2 cm to larger blocks up to 3 m in size. In contrast, boundaries between the syenite and the monzodiorite/monzonite do not show evidence of forceful intrusion. The syenite has a core of coarsely-crystalline material (feldspar laths greater than 3 cm in length), which is mantled for most of its length by more finely-crystalline material. Where the finer-grained mantle is absent, coarse-grained syenite is in direct contact with rocks of the pyroxenite/monzonite series. The syenite is characterized by a trachytic texture defined by primary alkali feldspar phenocrysts. Orientation of this foliation varies widely throughout the syenite, defining no apparent trend (see Enclosure 1). The whole of the complex, from pyroxenite to syenite, is cut by at least two sets of dykes, a plagioclase porphyry and a trachyte, which have similar trends, do not cross-cut each other and are probably coeval. Cross sections across the map-area are illustrated in Figure 1.4. These sections depict the orientation of contacts at the surface and are constrained by the intersection of structure contours with topography. The cross sections, are projected to a maximum depth of 100m, reflecting the uncertainty of the contact attitudes at depth. The cross sections provide a further tentative indication of the concentrically zoned nature of the pluton. Figure 1.4 - Cross sections across the Averill pluton -section lines as in Figure 1.4. numbered lithologies and Figure 1.4 - Cross sections across the Averill pluton - numbered lithologies and sect ion lines as in Figure 1.4. KR = Kettle River Formation. 11 Plate 1 - Brecciation of monzogabbro by syenite intrusions. Lens cap is 6 cm in diameter. 12 The rocks of the Averill pluton were emplaced prior to the mid-Eocene (see Appendix C) when the whole area was subjected to a period of extensional tectonism related to the formation of the Republic Graben in northern Washington (Cheney, 1980). In the area of the Franklin Camp, this period of rifting was followed by the rapid deposition of graben-fill sediments known as the Kettle River Formation, which unconformably overlie the Averill plutonics and Franklin Group (Little, 1957; Pinsent and Cannon, 1988). The Kettle River Formation comprises fanglomerates and arkoses, with locally capping rhyolites (Pinsent and Cannon, 1988). This period of rhyolitic volcanism ended the deposition of the Kettle River Formation and was followed by more extensive Eocene volcanism of the Phoenix Volcanic Group (Little, 1957). This group is locally represented by trachytes of the Eocene Marron Formation, commonly found capping mountain tops (Pinsent and Cannon, 1988). 1 3 2. PETROGRAPHY Thin sections of thirty-five rocks collected from the Averill plutonic complex have been examined. All are phaneritic. The freshest representative samples of each lithologic unit were selected for detailed analysis including electron microprobe (EMP) and whole rock chemical analysis. Mineral occurrences in each rock type are listed in Table 2.1. The table includes phases that were interpreted as primary and those interpreted as secondary or alteration products. Primary grains are defined as magmatic grains that display one or more of the following petrographic characteristics: i) ophitic, poikilitic or other igneous textures, ii) fresh, euhedral grains that do not exhibit replacement or overgrowth products, and iii) grains that have reaction rims and are partially or totally replaced by other igneous minerals. Secondary minerals are divided into those that are subsolidus igneous minerals that may form reaction rims around primary grains (biotite and hornblende), and metasomatic or alteration minerals (clay minerals). Petrographically they have the following characteristics: i) minerals that replace or partially replace primary grains, ii) minerals that overgrow primary grains, and iii) minerals that otherwise occur as alteration or breakdown products of primary minerals. Alteration is most commonly seen in the feldspars, which in many of thin sections show breakdown to unidentified clay minerals. From Table 2.1 it can be seen that the pyroxenite to monzonite series rocks comprise the primary phases: augite, hornblende, biotite, orthoclase, apatite, sphene and opaque phases (unidentified sulphides and oxides), with rare plagioclase. Secondary minerals common to this series are hornblende, opaque phases, and clay mineral alteration of feldspar. Primary minerals in the syenites are the same as in the pyroxenite-to-monzonrte series except for the addition of garnet and the absence of plagioclase. The secondary mineralogy of the syenites is the same as the pyroxenite to monzonite series. SAMPLE #/ROCK TYPE MINERALOGY 14 PRIMARY SECONDARY AUG HB BT OR PL PE GNT SP AP OP HB BT OP CHL C Q 11 1 X 0 X 0 0 0 0 X X X 0 0 X o 0 0 B5 1 X 0 X X 0 o 0 X X X 0 0 X 0 X 0 A l l 1 X 0 X X 0 o 0 o 0 X 0 0 0 X 0 0 10-1 2 X X X X X 0 0 X X X 0 0 X 0 X 0 10-2 2 x X X X X 0 0 X X X 0 0 X 0 X 0 432 2 x X 0 X 0 0 0 0 X X 0 0 X 0 X 0 A1B 2/3 X X X X X X 0 0 X X X 0 X 0 0 0 A1C 2/3 X X X X 0 X 0 0 X X 0 0 X 0 0 0 182A 2/3 X X X X 0 X 0 X 0 X X 0 X 0 0 X 182B 2/3 X X X X 0 0 0 X 0 X 0 0 X 0 0 0 433 2/3 X X 0 X o 0 0 0 X X X 0 X 0 X 0 436 2/3 X X 0 X 0 0 0 0 X X X 0 X 0 0 0 8 3 X X X X X 0 0 X X X X X X 0 X 0 182C 3 X 0 X X 0 0 0 0 0 X X X X 0 0 0 437 3 X X X X 0 0 0 0 X X X 0 X 0 X 0 438 3 X X X X o o 0 0 X X X 0 X 0 X 0 635 3 X 0 X X X 0 0 0 X X X 0 X 0 X 0 452C 3 X X 0 X o o o 0 X X 0 0 X X X 0 452E 3 X X 0 X o 0 0 0 X X 0 0 0 X X 0 452F 3 X X X X X 0 0 0 X X 0 0 0 0 X 0 449C 3 X X X X X X o 0 X X 0 0 X 0 X o 359 3/4 X 0 X X o o 0 0 X X X 0 X 0 X 0 449A 3/4 X 0 X X 0 o 0 o X X X 0 X 0 X 0 7 4 X X X X X o 0 0 X X X X X 0 X X 2 5 X X X X X o X X X X X 0 X 0 X 0 4-1 5 X 0 0 X X X X X X X 0 0 X 0 X 0 4-2 5 X 0 0 X X X X X X X 0 0 X 0 X 0 13 5 X 0 X X X X X X X X 0 0 X o X 0 B9 5 0 X X X 0 X 0 X X X 0 0 X o 0 0 451A 5 X X 0 X o o o o X X 0 0 o o o o 451B 5 X X X X o 0 o X X X X 0 X o X 0 588 5 X X X X 0 o 0 0 0 X X 0 o 0 X 0 6 6 0 0 X X X 0 0 0 0 0 0 0 X 0 X X 9 7 0 0 0 0 X o 0 0 0 0 0 0 0 X X X Table 2.1 - Table showing the mineral occurrences in each rock type. Sample number is followed by the rock type: 1 = Pyroxenite;2=Monzogabbro;3 = Monzodiorite;4=Monzonite;5=Syenite;6=Trachyte ;7 = Porphyry. Mineral abbreviations include:aug=augite; hb=hornblende; bt=biotite; or=orthoclase; pi=plagioclase; pe=perthite; gnt=garnet; sp=sphene; ap=apatite; op=opaques; chl=chlorite; c=calcite; q=quartz.. 15 These rocks were discriminated in the field on the basis of colour index and named according to Streckeisen (1975). 2.1. ALKALINE ROCK SERIES 2.1.1. Pyroxenite 2.1.1.1. Field Occurrence and Petrography The majority of pyroxenite outcrops are in the northwest corner of the map area, where they form a line of continuous bluffs 20 m in height, extending 200 m along strike. To the southeast is a thin discontinuous band of small outcrops. The pyroxenite is black on fresh and weathered surfaces but with weathering becomes friable due to the biotite in the rock. The unit is ultramafic (C.I. >90) and augite, biotite, alkali feldspar and sphene can all be recognized in hand sample. Where in contact with late syenites, the pyroxenite is commonly brecciated. Copper mineralization in the form of malachite staining and/or chalcopyrite is commonly associated with the pyroxenite/syenite contacts. In thin section the primary mineralogy comprises augite, biotite, minor alkali feldspar, sphene, apatite and opaque phases (Plate 2). Augite is the most common mineral, occurring as small anhedral grains and occasional larger euhedral phenocrysts. Augite crystals range in size from 0.5 mm to 2 mm and have pale to dark green pleochroism, and rare compositional zoning. The grains are commonly fractured but generally show very little mineralogic alteration. Strongly pleochroic biotite is closely associated with the accessory phases, sphene and apatite. Minor alkali feldspar is found as interstitial grains. The secondary minerals in the pyroxenite comprise unidentified sulphides and less abundant chlorite and calcite, commonly as veins. 16 oallnP\Par?r\ l^Zl9^^ PVroxenite s n o w i n9 phenocrysts with opaques and apatite. Field of view is 2 cm. 17 2.1.2. Monzogabbro 2.1.2.1. Field Occurrence and Petrography Monzogabbro outcrop is restricted entirely to the northwest corner of the map area, and is in contact with the pyroxenite to the east, and monzodiorite to the west. In the field monzogabbros were identified as mafic rocks (C.I.60-90). Minerals that were identified from hand sample include augite, amphibole and biotite. Dykes of cross-cutting syenite are noted in places. Monzogabbro mineralogy is the same as that of the pyroxenites, the major difference being in the proportion of phases. The primary mineralogy comprises augite, hornblende, biotite, alkali feldspar, apatite and opaque phases, with sphene and plagioclase occurring in some but not all samples. The augite grains are generally fresh phenocrysts. However in several samples, augite exhibits incipient replacement by secondary hornblende. Alkali feldspar is more common than plagioclase, and occurs in all samples as small phenocrysts and interstitial grains. Much of the feldspar has undergone alteration to unidentified clay minerals. Apatite is ubiquitous and is closely associated with the mafic phases. The secondary mineralogy consists of rare hornblende and biotite and late unidentified sulphide minerals. 2.1.3. Monzodiorite 2.1.3.1. Field Occurrence and Petrography Volumetrically, the monzodiorite unit is the most abundant lithology of the alkaline series. The rock is intermediate in Composition (C.I.30-60) and minerals identifiable in hand sample include augite, biotite, hornblende and alkali feldspar. Outcrop occurs largely as weathered, rounded patches on hillsides, and contacts with other units are not exposed although they may be inferred to within a few metres. 18 The primary mineralogy of the monzodiorites includes augite, biotite, hornblende, alkali feldspar, plagioclase, apatite and opaques, with rare sphene (Plate 3). Augite occurs as phenocrysts up to 3 mm in size which contain inclusions of felsic minerals, and grain boundaries may be replaced by hornblende. Biotite is also commonly replaced by hornblende. Felsic minerals occur as euhedral phenocrysts and as inclusions in the mafic grains. Apatite occurs as inclusions in all phases and as independent euhedral grains. Secondary minerals include hornblende, rare biotite, and unidentified sulphides, with sericitic alteration of the feldspars. 2.1.4. Monzonite 2.1.4.1. Field Occurrence and Petrography The monzonites (C.I.30-60) are the least voluminous of all the plutonic rocks of the Averill complex and represent the outermost shell of the concentrically zoned pluton. As such they occur only on the periphery of the map area, where they are found in contact with monzodiorites and older Mesozoic granitic plutons. In general the unit is poorly exposed and highly weathered. The primary mineralogy comprises phenocrysts of alkali feldspar and plagioclase, with interstitial augite and biotite and rare grains of quartz (Plate 4), Sphene and apatite are present as accessories. Secondary hornblende commonly replaces augite and biotite, and alteration of the feldspar produces unidentified clay minerals. 2.1.5. Syenite 2.1.5.1. Field Occurrence and Petrography The syenite occurs as an elongate northwest-southeast oriented intrusion consisting of a mantle of fine to medium grained syenite surrounding a coarse grained core. Many 19 20 Plate 4 - Photomicrograph of monzonite showing remnant augite grains, i plagioclase, alkali feldspar and quartz. Compare to Plate 2 to see range of variation between Units 1 and 4. Field of view is 2 cm. 21 outcrops display a strong trachytic texture defined by the parallel alignment of alkali feldspar, although the orientation of the foliation varies throughout the intrusion (see Enclosure 1). The syenite intrudes the pyroxenites, monzogabbros and monzodiorites, creating zones of brecciation. Many cross-cutting dykes of syenite are also visible throughout the area, varying in scale from millimetres to several metres thick. Where observed, the dyke orientation parallels the elongation direction of the Averill pluton. The primary mineralogy of the syenites includes alkali feldspar, augite, biotite, hornblende, poikilitic garnet, sphene and apatite (Plate 5). The alkali feldspar crystals have a trachytic texture with phenocrysts ranging in size from 1cm to 8cm. Poikilitic garnet is an interstitial phase which mantles all the mafic phases. It occurs as a reddish/orange isotropic mineral and is unique to the syenites. The poikilitic nature of the garnet, along with the absence of metamorphic chlorite and biotite suggests that the garnet constitutes part of the primary mineralogy and is not a product of regional metamorphism. Apatite and sphene have a close association with the mafic minerals and garnet. Secondary hornblende commonly replaces both the augite and the biotite, and clay minerals are abundant due to the alteration of feldspar. 2.2. DYKES 2.2.1. Trachyte 2.2.1.1. Field Occurrence and Petrography Trachyte dykes are buff coloured and form rubbly outcrops. They are rarely traceable for more than a few metres. They range in width from 1m to 5m, and have an azimuth between 000° and 020°. Trachyte dykes can be seen cross-cutting all of the rocks of the alkaline series. Plate 5 - Photomicrograph of poikilitic garnet in syenite. Note enclosed augite and feldspar. Field of view is 2 cm. 23 In thin section the trachyte dyke rocks consist mainly of alkali feldspar, which has been highly weathered. Recognizable primary mineralogy includes alkali feldspar, with less abundant biotite, plagioclase and quartz. Later pyrite and chalcopyrite are also found in isolated patches within these dykes. 2.2.2. Porphyry 2.2.2.1. Field Occurrence and Petrography Porphyry dykes are the least abundant rock types of Averill complex, and they are also the most distinctive, having a grey, spotty weathered surface. Outcrops are few and contacts are rarely observed. Outcrops tend to be rubbly and small (<2m). Porphyry dykes have a trend similar to the trachyte dykes although they are dominantly oriented towards 000° azimuth. The porphyry dykes cross-cut most of the units of the alkaline series, but do not intersect the trachyte dykes, suggesting that the two events of dyke emplacement may be coeval. These rocks are the most altered of all of the rock types of the complex with all of the phenocryst phases being replaced. Postulated primary mineralogy, based on the nature of the alteration, includes plagioclase and biotite. The majority of the rock comprises unidentified clay minerals deriving from the breakdown of felsic minerals in the rock (Plate 6). 2.3. S U M M A R Y Rocks of the Averill pluton are gradational in composition between pyroxenite and monzonite, with changes between units being marked by small changes in colour index, and less commonly grain size. The gradational nature and the outcrop pattern suggest a close genetic relationship. The map pattern of Units 1 to 4 suggests a concentric zonation (Figure 2.1) from pyroxenite (Unit 1) at the centre, through monzogabbro and Plate 6 - Photomicrograph to show weathered, altered grains within Unit 7 This texture is unique to the suite. Field of view is 2 cm. Figure 2.1 - Schematic diagram showing pluton zonation and postulated petrogenetic origin of pluton. Numbered lithologies as in Figure 1.4. 2 6 monzodiorite (Units 2 and 3), to monzonite (Unit 4) on the outside. The syenite (Unit 5) has intruded the centre of this gradational suite, cutting Units 1 and 2. Units 3 and 4 do not show evidence of forceful intrusion by the syenite. The syenite comprises both a coarsely-crystalline core, and a mantle of finer material. The fine grained mantle represents the bulk of the syenitic material, and only in the very northern end of the map area does it fail to mantle the coarse core material. Later faulting has created two structurally controlled outliers from the main suite (Pinsent and Cannon, 1988). The smaller of the two (Figure 2.2) comprises rocks from Units 1, 3 and 5, and does not display recognizable concentric zoning. Small outcrops of Unit 1 are mantled by Unit 3 to the south, and are intruded by Unit 5 to the north. The second outlier, to the east of the map area (Figure 2.3) also has a map pattern where the lithologies are zoned with the syenite of Unit 5 intruding through the middle of Unit 3. A small amount of pyroxenite (Unit 1) outcrops, but is poorly exposed, and Units 2 and 4 are missing from the sequence at this location. Two later dyke swarms cross cut all of the alkaline plutonic rocks of the Averill suite. Cross sections across the map area are shown in Figure 1.4. 27 118*21' _ l 118°20' Trachyte Kettle River Fm. pTrachyte 49*34' Figure 2.2 - Geology of the westernmost structurally controlled outlier.v«»=fautts. 28 Figure 2.3 - Geology of the easternmost structurally controlled outlier.^=faults. 29 3. MINERAL CHEMISTRY 3.1. ELECTRON MICROPROBE ANALYSIS All primary mineral phases were analyzed with a Cameca SX-50 electron microprobe at the University of British Columbia. Samples were prepared as one inch round thin sections, which were polished and then carbon coated. Prior to carbon coating, each thin section was examined using a petrographic microscope, and individual grains of interest were marked. Marking grains and traverses prior to carbon coating facilitates locating the grains to be analyzed once the sample is loaded into the machine. EMP analysis of the various mineral groups was performed over a six month period. 3.1.1. Operating Conditions The EMP was run with an accelerating potential of 15 Kv and a beam current of 20 nanoamps for all analyses. The beam diameter varied for different mineral groups. For the pyroxene and garnet analyses, grains were analyzed with a beam diameter of 3.6 microns, whereas analyses for biotite, amphiboles, feldspars, apatite and sphene were performed with a beam diameter of 5 microns. All elements were analyzed using the K-alpha spectra, except Sr and Ba which used L-alpha (Cameca Reference Guide). The standards used for calibration had compositions similar to the unknown minerals. For the majority of analyses, the EMP was run in integral mode, meaning that counting windows and baselines are automatically set by the software. Pyroxene and garnet analyses were performed with the machine in differential mode, requiring counting windows and baselines to be set by the operator. During EMP operation, room and instrument temperature, gas pressure (for venting the machine), vacuum and spectrometer biases have to be met to ensure ideal operation of the machine. These conditions are tabulated in Table 3.1. Table 3.1 - Electron Microprobe operating conditions Water: In 50 Kpa Out 40 Kpa Temp. 16°C P 10 Gaa: P tank >3000 Kpa P bleed 280 Kpa N Gas: P tank > 500 p s i P bleed 3 p s i Temp: Room 22°C Cabinet 23°C Vacuum: PCOL lE-lpa Spec Xtal Bias +/-20V ARLK lE+5pa 1 LiF 1820 PWDS 8E+0pa 2 TAP 1435 SCOL 2E-4pa 3 PET 1955 GUN 2E-5pa 4 TAP 1440 Table 3.1 - Electron microprobe operating conditions. P=pressure; P10 gas = 10% methane in argon; N gas=nitrogen gas used to vent the machine; ARLK=airlock, measured in atmospheric pressure; PWDS=value of pressure inside the spectrometers; SCOl_=the value of the secondary vacuum in the column; GUN = value of the pressure inside the electron gun. o 31 3.1.2. Analytical Conditions The compositions of seven mineral groups were measured with the electron microprobe, including pyroxene, garnet, biotite, amphibole, feldspar, apatite and sphene. Analytical conditions used for each mineral group are tabulated, including details of calibration standards, spectrometers, lines, peak positions and background stepoffs, counting times and counts per second for each element (Tables 3.2 to 3.6). The same analytical conditions were used for standards and unknowns. The EMP at the University of British Columbia has several computer programs designed to facilitate data aquisition and reduction. Each program has options which correspond to different mineral groups. For example, "GEO" automatically recalculates iron to FeO.calculates oxygen by stoichiometry and reports the analysis in oxide equivalents. Pyroxene and garnet analyses were reduced using this program. An alternate program, "QUANTI", is based on mineral stoichiometry and calculates oxygen by difference, giving the final output as element weight per cent. Analyses of mica, amphibole, feldspar apatite and sphene were reduced using this program. "QUANTI" was found to be more suitable than "GEO" for several of the mineral groups analyses. A total of 17 EMP calibration standards were used. Tables 3.2 to 3.6 list the standards used for each mineral group, and compositions of these standards are given in Table 3.7. TABLE 3.2: PROBE SETUP AND STANDARD8 USED FOR  PYROXENE AND GARNET KV 15 Current 20 Beam diameter 3.6 microns XTAL: Spec 1 (HP) L i F ; Spec 2 (LP) TAP; Spec 3 (HP) PET; Spec 4 (LP) TAP. E l Line Std Name Std# Spec X t a l Peak pos +Bkg (high) -Bkg/ Slope Time sec Cps / s t d S i Ka AUGITE P220 4 TAP 27754 850 850 10 345 T i Ka AMPHIBOLE A229 3 PET 31451 600 600 10 16.9 A l Ka AMPHIBOLE A229 2 TAP 32462 1100 1100 10 117 Fe Ka AEGIRINE P246 1 LIF 48081 850 850 10 35.8 Mn Ka P-MANGITE P245 1 LIF 52196 600 600 10 54.2 Mg Ka AUGITE P220 2 TAP 38490 1600 1600 10 124 Ca Ka DIOPSIDE P379 3 PET 41175 600 600 10 102 Na Ka AEGIRINE P246 4 TAP 46307 700 700 10 47.9 1) LP are most e f f i c i e n t f o r energies <2.6KeV. 2) Background = slope * Background(High). Table 3.2 - Electron microprobe analytical conditions for pyroxene and garnet. P-mangite=pyroxmangite. TABLE 3.3: PROBK SKTDP AND STANDARDS DSBD FOR  BIOTITE AMD AMPHIBOLE KV 15 Current 20 Beam diameter 5 microns. XTAL: Spec 1 (HP) LiF; Spec 2 (LP) TAP; Spec 3 (HP) PET; Spec 4 (LP) TAP. E l Line Std Name Std# Spec Xtal Peak pos +Bkg (high) -Bkg/ Slope Time sec Cps /std Si Ka F-PHLOGO M24 2 TAP 27750 800 800 10 326 Ti Ka AMPHIBOLE A229 1 LIF 68261 600 600 20 2.83 Al Ka ALBITE F20 4 TAP 32463 1000 1000 10 155 Fe Ka AEGIRINE P246 1 LIF 48090 500 500 10 36.4 Mn Ka P-MANGITE P245 1 LIF 52200 600 600 10 62.4 Mg Ka F-PHLOGO M24 2 TAP 38499 1600 1600 10 220 Ca Ka AMPHIBOLE A229 3 PET 38374 600 600 10 42.4 Na Ka ALBITE F20 2 TAP 46363 700 700 10 52.7 K Ka ORTHOCLASl : F96 3 PET 42765 600 600 10 62.5 F Ka F-PHLOGO M24 4 TAP 71315 770 770 20 3.34 Cl Ka KCl C286 3 PET 54040 600 600 20 173 1) LP are most e f f i c i e n t for energies <2.6KeV. 2) Background = slope * Background(Hiqh)-Table 3.3 - Electron microprobe analytical conditions for biotite and amphibole. F-phlogo=fluor-phlogopite; p-mangite=pyroxmangite; KCl=potassium chloride. TABLE 3.4: PROBE SETUP AND STANDARDS USED FOR  FELDSPAR KV 15 Current 20 Beam Diameter 5 microns. X t a l : Spec 1 (HP) L i F ; Spec 2 (LP) TAP; Spec 3 (HP) L i F ; Spec 4 (LP) TAP. E l Line Std Name Std# Spec X t a l Peak pos +Bkg (high) -Bkg/ Slope Time sec Cps / s t d S i Ka ANORTH F365 4 TAP 27747 800 800 10 447 A l Ka BYTOWN F367 4 TAP 32451 1000 1000 10 259 Fe Ka AUGITE P220 1 LIF 48081 500 500 10 8.55 Mg Ka AUGITE P220 2 TAP 38496 1000 1000 10 127 Ca Ka BYTOWN F367 3 PET 38386 600 600 10 6618 Ba La BARITE E16 1 LIF 68938 500 500 30 7. 95 Na Ka ANORTH F365 2 TAP 46344 700 700 10 47.5 K Ka MICROCLIN F276 3 PET 42744 600 600 10 62.5 Sr La STRONTIAN S23 2 TAP 26716 450 450 30 383 1) LP are most e f f i c i e n t f o r energies <2.6KeV. 2) Background = slope * Background(High). Table 3.4 - Electron microprobe analytical conditions for feldspar. Anorth = anorthoclase; bytown=bytownite; microclin=microcline; strontian=strontianite. TABLK 3.5: PROBE SKTDP AND STANDARDS DSKD FOR  APATITE KV 15 Current 20 Beam diameter 5 microns. XTAL: Spec 1 (HP) L i F ; Spec 2 (LP) TAP; Spec 3 (HP) PET; Spec 4 (LP) TAP. E l Line Std Name Std# Spec X t a l Peak pos +Bkg (high) -Bkg/ Slope Time sec Cps / s t d S i Ka SPHENE O120 2 TAP 27731 800 800 10 526 Ca Ka APATITE O03 3 PET 38380 600 600 10 237 Na Ka ALBITE F20 4 TAP 46294 700 700 20 57.4 P Ka APATITE O03 2 TAP 23957 750 750 10 274 F Ka FLUORITE O02 4 TAP 71194 770 770 20 19.9 1) LP are most e f f i c i e n t f o r en e r g i e s <2.6KeV. 2) Background = slope * Background(High). Table 3.5 - Electron microprobe analytical conditions for apatite. TABLE 3.6: PROBE SETUP AND STANDARDS USED FOR SPHENE KV 15 Current 20 Beam diameter 5 microns. XTAL: Spec 1 (HP) L i F ; Spec 2 (LP) TAP; Spec 3 (HP) L i F ; Spec 4 (LP) TAP. E l L i n e Std Name Std# Spec X t a l Peak pos +Bkg (high) -Bkg/ Slope Time sec Cps / s t d S i Ka SPHENE O120 2 TAP 27735 800 800 10 248 T i Ka SPHENE O120 1 LIF 68281 600 600 10 20.1 A l Ka ALBITE F20 4 TAP 32430 1000 1000 10 157 Fe Ka ILMENITE 0231 1 LIF 48080 500 500 10 66.1 Ca Ka APATITE O03 3 PET 38380 600 600 10 238 Na Ka ALBITE F20 4 TAP 46294 700 700 20 57.4 F Ka FLUORITE O02 4 TAP 71194 770 770 20 19.9 1) LP are most e f f i c i e n t f o r energies <2.6KeV. 2) Background = slope * Background(High). Table 3.6 - Electron microprobe analytical conditions for sphene. Table 3.7 - Reported analyses of standards. A229 C286 216 F20 F96 F276 365 F367 Si 18.87 0.00 0.00 32.16 29.64 30.03 30.47 22.97 Ti 2.83 0.00 0.00 0.00 0.00 0.03 0.00 0.00 Al 7.88 0.00 0.00 10.26 10.18 9.68 11.09 16.95 Fe2 2.31 0.00 0.00 0.02 0.07 0.03 0.00 0.00 Fe3 6.78 0.00 0.00 0.00 0.00 0.02 0.14 0.27 Mn 0.07 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Mg 7.72 0.00 0.00 0.01 0.00 0.01 0.02 0.00 Ca 7.36 0.00 0.00 0.03 0.05 0.96 0.97 11.10 Na 1.93 0.00 0.00 8.75 0.26 12.56 6.46 1.92 K 1.70 53.16 0.00 0.00 12.73 0.01 2.64 0.00 Ba 0.00 0.00 65.70 0.00 0.55 0.00 0.16 0.00 F 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 P 0.00 0.00 0.00 0.00 0.21 0.00 0.00 0.00 Sr 0.00 0.00 0.00 0.00 0.01 0.00 0.27 0.00 V 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 As 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Cl 0.00 46.84 0.00 0.00 0.00 0.00 0.00 0.00 o 43.05 0.00 0.00 48.86 45.96 45.78 47.98 46.43 s 34.30 TOTAL 100.02 100.00 100.00 100.10 99.72 99.14 100.70 99.67 O03 0231 S i 0.16 0.00 T i 0.00 27.40 A l 0.03 0.00 F«2 0.09 8.11 F«3 0.00 28.06 Mn 0.01 3.69 Mg 0.01 0.18 Ca 38.61 0.00 Na 0.17 0.00 K 0.01 0.00 Ba 0.00 0.00 F 3.53 0.00 P 17.84 0.00 s r 0.05 0.00 V 0.01 0.00 As 0.06 0.00 C l 0.41 0.00 C02 0 38.29 31.30 Tota l 99.23 99.40 P220 P24S P246 23.71 22.41 24.28 0.44 0.00 0.18 4.62 0.01 0.54 0.00 0.00 0.00 6.34 3.68 27.96 0.10 32.06 0.00 10.04 2.67 0.25 11.31 0.71 1.00 0.94 0.00 9.79 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00. 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 44.42 37.99 41.59 100.52 99.56 99.41 P379 023 M24 25.88 0.00 19.97 0.04 0.00 0.00 0.04 0.00 6.58 0.00 0.00 0.03 0.04 0.00 0.00 0.04 0.00 0.01 11.22 0.00 17.23 18.38 2.83 0.00 0.02 0.00 0.07 0.01 0.00 9.25 0.00 0.00 0.00 0.00 0.00 9.04 0.00 0.00 0.00 0.00 55.20 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 8.39 44.32 33.57 41.88 100.04 100.00 104.05 Table 3.7 - Chemical analyses in atomic per cent of all of the standards used in the various analyses. 38 3.1.3. Detection limits, analytical accuracy and precision In all cases the minimum detection limit for each element was estimated as three times the background counts (Nicholls and Stout, 1988), or D.L = 3 (BKG) Elemental concentrations that fell below detection are reported as "-" in Appendix A. Analytical precision was estimated from the variance of replicate analyses of standards over a period of several days. The variance calculated from these analyses therefore incorporates the effects of instrument drift, which was found to be minimal. Where reported, minimum analytical precision is reported as one standard deviation, calculated from; s 2 = S ( x r x ) 2 N-1 where S 2 = the sample variance; Xj = the ith measured concentration; X = the' mean concentration of the oxide for all analyses; and N = the number of analyses. The accuracy of the EMP analyses is difficult to estimate quantitatively. The published analyses of the standards are regarded as true, and the only control on accuracy is how well these "true" analyses can be reproduced. During alLof the analyses reported in this thesis, a standard was used which was not involved with the calibration. After calibration was complete, the standards were analyzed and accuracy was taken as acceptable if the analytical total was within 1% of the reported value. 3.2. CHAIN SILICATES An average of 20 analyses per grain were made on all samples, and where possible these included both core and rim analyses. 39 3.2.1. Pyroxene Pyroxenes in each sample were analyzed for the elements Si, Ti, Al, Fe, Mn, Mg, Ca, and Na. Ni and Cr were found to be below detection in all samples. The clinopyroxene compositions from the Averill alkaline complex are similar. Figures 3.1 a and 3.1 b illustrate the range of pyroxene compositions found in Units 1 to 4 and Unit 5 respectively. All of the compositions fall within the range of augite/salite. There is little between-grain or between-sample variation, however chemical zoning is present within individual grains in a few samples (samples 8 and 2, Figure 3.1). The highest magnesium pyroxenes are found in Units 1 to 4, while high iron content is associated with the Unit 5. Pyroxene analyses from each lithology are listed in Appendix A. In each case the most magnesium-rich and the most iron-rich analyses are presented. These analyses are taken as being representative of the pyroxenes found in rocks of the Averill alkaline complex. 3.2.2. Amphibole Amphiboles in each sample were analyzed for the elements Si, Ti,AI, Fe, Mn, Mg, Ca, Na, K, F and Cl. Cl was detected in all samples. The amphiboles are hornblende and exhibit little to no chemical zonation within or between grains. Between sample variation is small and is reflected in the concentrations of Fe and Mg. Mg concentration is lower in Units 1 and 2 (5-6 wt.%) than in Units 3 and 4 (8-10 wt.%). Unit 5 has the least magnesian amphiboles (4 wt.%). Fe content of the amphiboles varies in the opposite sense to magnesium. Amphiboles of Units 1 and 2 have higher iron contents (13-14 wt.%) than those of Units 3 and 4 (7-10 wt.%). Amphiboles of Unit 5 contain up to 7 wt.% iron in the amphiboles. Amphibole analyses are reported without hydrogen and consequently sum to 98%. The remaining 2wt.% can be attributed to OH. 40 CaMg8l20 Q . CaFe8l2Oa Figure 3.1 - Pyroxene quadrilateral diagrams showing the composition of pyroxene. The diagrams do not show complete quadrilaterals, and the labateocr the upper and lower right hand side of each diagram refer to apices at the farright comer of the quadrilateral. Figure 3.1 a shows analyses from Units 1 to 4; figures 3.1b shows analyses from Unit 5. 41 Representative analyses of the most iron and the most magnesium rich amphiboles from each lithology are given in Appendix A . 3.3. GARNET Garnets found in the syenites were analyzed for the elements Si, Ti, Al, Fe, Mn, Mg, and Ca. Cr and Ni were below detection in all samples. Garnets are only present in the syenite unit. No within or between grain variation was found, and there was no variation between samples. The garnet composition is andradite. During data reduction (see Appendix A) the Fe was partitioned to F e + 2 and F e + 3 . The resulting mineral structural formulae do not contain F e + 2 , indicating that all of the Fe in the garnets is as F e + 3 . This has resulted in high wt.% totals (101 -102.5) for the garnet analyses. Average analyses from each lithology are reported in Appendix A. 3.4. BIOTITES Biotites were analyzed for the elements Si, Ti, Al, Fe, Mn, Mg, Na, K, F and Cl. Cl was detected in all of the samples. Compositionally the biotites show little or no within-or between- grain variation. Small variations between samples are observed in Fe (12% to 15%). The biotites show little or no variation in Mg and Fe. Biotite analyses are reported without hydrogen as OH and consequently sum to approximately 95%. The remaining 5 wt.% can be attributed to OH. Representative analyses of the most iron and the most magnesium rich biotites from each lithology are given in Appendix A 3.5. FELDSPARS Feldspars in each sample were analyzed for the elements Si, Al Fe, Mg, Ca, Na, Ba, and K. Sr was below detection in all samples. Up to 20 spots were analyzed in each sample to characterize the range of chemical zoning in the feldspars. Chemical zonation 3.2a 42 11 AngoAb^ o „ / / Ab^ / • %m+**m \ Or 0.0 I I 0.2 0.4 0.6 0.8 l.O 3.2b 10-2 '•s AnsoAbso °"J \ ° J / \ °° T • 0.0 0.2/ 0.'* 0.6 \).8 1.0 10-1 % •• \ Or 0.0 0-2 0.* 0.6 0.8 1.0 Figure 3.2 - Feldspar composition diagrams on distorted Ab*An-Or triangtes. 3.2a=pyroxenites; 3.2b=monzogabbro; 3.2c=rrx>nzodkxite; 3.2d=rrx)nzonite; 3.2e=syenite. The triangles are terminated at 50% along the Ab-An axis, with the top aptee representing the point A b g g A i ^ 13 A n 5 0 A b 5 0 3.2e 45 varied between samples and was different for plagioclase and alkali feldspars. The range of chemical variation is illustrated in Figure 3.2. 3.5.1. Alkali Feldspar Series 3.5.1.1. Units 1-4. In Unit 1 alkali feldspar solid solution exists between Or100 and Or40. In Units 2 to 4, this solid solution series is replaced by a more abrupt division between approximately Or90 to approximately Or10. This distribution is particularly well displayed in samples 10-2 and 7 in Figure 3.2. Samples 10-1 and 635 in the same figure show that the Ab end of the solution may vary as much as up to Or50. Representative analyses of the most sodic and the most alkalic feldspars from each of the samples shown in Figure 3.2 are presented in Appendix A. 3.5.1.2. Unit 5 Alkali feldspar solid solution in Unit 5 is restricted to a compositional range between Or100 and Or70. Sample 13 contains up to 1% Ca. This sample is taken from one of the coarsely-crystalline core areas of Unit 5. Individual feldspar laths in rocks of this core material range in length from 4 cm to 8 cm, the largest grains being almost 1 cm wide. EMP analyses representing the most Na and K rich alkali feldspars from each sample of Unit 5 are presented in Appendix A. 3.5.2. Plagioclase Series Plagioclase feldspar is rare or absent in rocks of Units 1 and 2. In Unit 3 solid solution between An and Ab is well developed, with compositions up to An50. The lack of compositions between An20 and An30 may be representative of part of the peristerite solvus. Examples of the most Ab and Na rich plagioclase feldspars are presented in Appendix A. 46 3.6. ACCESSORY MINERALS The accessory minerals analyzed with the electron microprobe are apatite and sphene. Apatite is ubiquitous in all lithologies, whereas the sphene analyses are from Unit 5 (syenite) alone. Although sphene is present in the more mafic units (Unit 1 especially) the sphene grains in these rocks were too altered to yield good analyses. 3.6.1. Apatite Apatite grains were analyzed for the elements Si, Ca, P and F. Up to 15 spots were analyses on each grain and core and rim analyzed were obtained where possible. The composition of the apatite grains varies only with respect to silica. Silica is at or below detection in apatites from Units 1 to 4, but is noticeably above detection in apatites from Unit 5. Average analyses of apatite grains from Units 1 to 5 are presented in Appendix A 3.6.2. Sphene Sphenes were analyzed for the elements Si, Ti, Al, Fe, Ca and Na. F was below detection in all samples. Up to 15 spots were analyzed on each grain and where possible, analyses of cores and rims were taken. Many of the grains were too small to obtain separate core and rim analyses. No chemical variation was found in the sphene grains. The oxygens totals are made to sum to five, to compensate for the lack of other anions. Average analyses of sphene grains from Unit 5 are presented in Appendix A. 47 4. GEOCHEMISTRY 4.1. MA JOR ELEMENTS Major element chemical analysis was performed using X-ray fluorescence spectrometry, on a Phillips 1410 spectrometer at The University of British Columbia. Details of samples preparation are given in Appendix B. Whole rock geochemical data is presented in Table 4.1. Analytical precision for these data is estimated as 1 standard deviation. 4.1.1. Major and minor element distribution Harker diagrams showing the chemical variation in rocks of the Averill complex are shown in Figure 4.1. The rocks range in S i 0 2 content from 45% and 65%, indicating that the rocks range from basic to intermediate in composition (Hyndman, 1972). There is a continuous trend of either depletion or enrichment of elements between pyroxenite and syenite (Figure 4.1). The trachyte and porphyry dykes parallel this trend. In general major element variations show lower concentrations of FeO, MgO, T i 0 2 , MnO, CaO and P 2 0 s with increasing silica content, while AI2O3, N a 2 0 and K 2 0 all increase with increasing silica content (Figure 4.1). These trends are largely to be expected during magmatic differentiation (Bowen, 1952). The reduction of P 2 0 5 concentration with increasing silica content is the only trend that does not strictly adhere to Bowen's reaction series. P 2 O s is most commonly present in apatite (or monazite) which tends to crystallize late (Hyndman, 1972), and as such would be expected to increase with increasing S i 0 2 content until it crystallized. The decrease of P 2 0 5 with increasing silica content, and its presence in all of the rocks of the Averill complex suggests that apatite started crystallizing at an early stage of pluton evolution. O o CN — O Oo_| c 0) | o ° c 12 °3S 9 D t o o o - f — — r 35 40 45 50 55 60 6 3 .0 SiC2 o o a 35 40 45 50 55 60 65 Si02 - 1 70 a a , I 1— 40 45 • 50- 55 60 65 701 Si02 9 r , D aa 35 ' 40 45 I 1— 50 55 Si02 60 65 70 O CM O 35 o 35 o CN CL „ o. 635 a a —t— 40 45 50 55 Si02 60 65 70 • • • • B a 1 40 45 50 55 Si02 60 70 O • • • • • 40 45 50 Si02 1 -i 1 1 55 60 65 70 0 Unftl • Unit82 3and4 X Units A Unite + Unit7 Figure 4.1 - Harker diagrams showing whole rock major element chemical variation with respect to Si02 for the Averill suite. 4.1a=Ti02> AJ2O3, FeO, MnO, MgO: 4.1b=CaO, Na2Ot K2Ot P205. 49 All oxides show either continuous increase or decrease in oxide concentrations between pyroxenite and syenite, as evidenced by the curvilinear trends of the data in Figure 4.1. Continuous reduction is shown by FeO, MgO, T i0 2 , MnO, CaO and P2O5, while continuous increase is shown by AI2O3, Na20 and K 2 0 . Whole rock chemical data has been used to calculate CIPW norms for all of the rocks of the Averill complex. All the rocks are strongly undersaturated with respect to silica, with the exception of the porphyry dykes of Unit 7. The rocks range in composition from strongly nepheline and leucite normative for the pyroxenites, through nepheline normative for the monzodiorites to syenites, to weakly quartz normative (peralkaline) for the trachyte dykes. All norms were calculated with iron as FeO. 4.1.2. Chemical Trends The rocks of the Averill Plutonic Complex have alkaline chemical characteristics (Figure 4.2) (Macdonald and Katsura, 1964). The only exception is sample 9, which is a feldspar porphyry dyke, and is also petrographically distinct from the rest of the rocks of the Averill suite. Chemically, rocks range from mildly alkaline to strongly alkaline for Unit 5. An AFM illustrates the high FeO concentration with respect to MgO which is characteristic of the Averill complex (Fig 4.3). Compared to other known alkaline intrusions, such as the Kruger syenite in southern British Columbia (Currie, 1976), rocks of the Averill complex again show unusually high FeO concentration (Figure 4.4). When compared to other subalkaline volcanic series, such as the Thingmuli volcanic rock series of Iceland (Carmichael, 1964) the Averill rocks again show high Fe concentration but generally follow the same trend (Figure 4.5). However, the Thingmuli rocks represent a greater extent of differentiation and have lower concentrations of Fe at both extremes of differentiation. Figure 4.2 - Alkalis vs. silica diagram showing the alkaline affinity of the rocks of the Averill suite. Symbols for different rock units as Figure 4.1. Boundary between alkali and tholeitic from Macdonald and Katsura, 1964. Ul o Figure 4.3 - AFM diagram showing the chemical affinity and differentiation trend of the Averill complex. Note high FeO concentration with respect to MgO. Symbols as in Figure 4.1. F Figure 4.4 - AFM diagram showing comparison of Averill data to that of the Kruger syenite, southern B.C. (Currie, 1979). Note again strong FeO enrichment of Averill rocks with respect to Kruger.O=Averill rocks;•= Kruger suite. m to F Figure 4^ 5 - AFM diagram comparing the Averill suite with Thingmuli volcano, Iceland (Carrriichael, 1964). Averill rocks show the same extent of FeO enrichment and follow the same general trend. 0=Averill rocks;d=Thlngmuli suite. u> 54 4.1.3. Differentiation Processes Mineralogically Units 1 to 4 are similar. The differences lie in colour index alone. Field evidence (Chapter 2) also suggests that these rocks are gradational to one another. These observations indicate that rocks of the Averill suite could be related through simple crystal fractionation. To date, the best method to test this hypothesis rigorously uses Pearce element ratio diagrams, where ratios (or combinations of ratios) of element fractions are plotted as X and Y axes in order to parallel the mineral element stoichiometry. It is implicit that the denominator constituent of the ratios is conserved during the igneous process (Russell and Nicholls, 1988). 4.7.3 .7 . Units 1 to 4 The petrographic and field evidence, along with the whole rock geochemical data must be used to infer the igneous process responsible for the differentiation trend established between Units 1 and 4. The rocks are gradational between pyroxenite and monzonite in terms of contact relationships, petrography and whole rock geochemistry. Petrography shows a progressive decrease in pyroxene, amphibole, biotite and sphene between the pyroxenite and monzonite, with an associated progressive increase in plagioclase and alkali feldspar. Whole rock geochemical data (Table 4 .1) also shows that from the pyroxenite to the monzonite there is a progressive decrease in oxides consistent with the crystallization of pyroxene, amphibole, biotite, apatite and sphene (Section 4.1.1.) , with corresponding increase in oxides consistent with the remaining feldspar. On the basis of these observations it can be strongly suggested that the rocks of Units 1 to 4 are related by simple crystal fractionation involving the minerals augite, biotite and hornblende. Pearce element ratio diagrams cannot be used in the case of Units 1 to 3 as no elements are conserved (Russell and Nicholls, 1988) . Sample A l l - 1 A l l - 2 1 1 - 1 11-2 1 0 - 2 - 1 1 0 - 2 - 2 1 0 - 1 - 1 1 0 - 1 - 2 S Unit 1 1 1 1 2 2 2 2 SiO, 4 2 . 84 4 3 . 51 4 4 . 33 4 4 . 3 9 5 0 . 1 7 50 . 10 4 3 . 30 4 3 . 13 . 4 5 1 TiOj 1. 89 1. 92 2 . 31 2 . 3 3 0 . 7 7 0 . 75 0 . 97 0 . 97 . 0 0 5 A l , 6 3 5. 79 5 . 70 5 . 68 5 . 6 7 1 4 . 9 6 14. 98 12 . 70 12 . 70 .112 FeO J 1 7 . 53 17 . 10 1 7 . 65 1 7 . 6 7 1 0 . 2 5 10 . 31 13 . 84 1 3 . 83 . 197 MnO 0. 43 0. 43 0. 45 0 . 4 3 0 . 2 2 0. 21 0. 25 0 . 24 .004 MgO 8. 11 8 . 22 7 . 70 7 . 6 4 7 . 3 9 7 . 50 9 . 73 9 . 59 . 133 CaO 19 . 16 19 . 35 2 1 . 23 2 1 . 3 0 1 1 . 4 9 11 . 46 13 . 53 13 . 55 . 083 Na,0 1. 43 1. 45 1. 74 1 . 6 5 3 . 0 4 2 . 79 1. 19 1. 20 . 0 4 1 K 2 6 1. 13 1. 16 0 . 54 0 . 5 4 2 . 8 1 2 . 38 2 . 99 2 . 99 .004 P 2 ° 5 1. 17 1. 18 1 . 33 1 .34 0 . 7 7 0 . 69 1. 06 1 . 06 . 003 L 6 I 0 . 05 0 . 05 0 . 04 0 . 0 4 0 . 0 4 0. 04 0 . 09 0 . 10 Tot 9 9 . 49 100 . 02 102 . 95 1 0 2 . 9 7 1 0 1 . 8 7 101 . 17 9 9 . 57 9 9 . 28 Ba 470 437 47 39 1153 1106 1407 1394 Cr 125 129 68 59 112 119 127 150 Nb 13 13 13 13 13 13 13 13 Ni 89 88 61 55 60 63 80 92 Rb 51 50 9 9 94 91 128 129 Sr 611 618 558 554 1773 1800 2518 2580 V 664 675 738 733 432 420 565 554 Y 69 70 92 89 23 22 24 32 Zr 235 237 263 267 60 62 83 84 OR 0 . 0 0 . 0 (AB) 0 . 0 0 . 0 (AN) 6 . 0 5 . 6 P L 6 . 0 5 . 6 L C 5 .2 5 . 3 N E 6 . 5 6 . 6 (WO) 2 5 . 0 2 6 . 3 (EN) 1 0 . 1 1 0 . 9 (FS) 1 5 . 0 1 5 . 5 DI 5 0 . 2 5 2 . 9 (FO) 7 . 0 6 . 6 (FA) 1 1 . 4 1 0 . 4 O L 1 8 . 4 1 7 . 0 CS 6 . 6 6 . 0 I L 3 . 5 3 . 6 A P 2 3 . 7 2 . 7 0 . 0 0 . 0 1 6 . 6 0 . 0 0 . 0 1 1 . 0 6 . 0 6 .4 1 8 . 8 6 . 0 6 .4 2 9 . 9 2 . 5 2 . 5 -7 . 9 7 . 5 7 . 9 2 8 . 4 2 8 . 7 1 3 . 8 1 1 . 3 1 1 . 4 6 . 8 1 7 . 4 1 7 . 6 6 . 6 5 7 . 2 5 7 . 7 2 7 . 3 5 . 4 5 . 3 8 . 0 9 . 2 9 . 0 8 . 7 1 4 . 7 1 4 . 4 1 6 . 8 6 . 9 6 . 6 -4 . 3 4 . 4 1.4 3 . 1 3 . 1 1 .8 1 4 . 0 0 . 0 0 . 0 14 .4 0 . 0 0 . 0 2 1 . 3 2 0 . 4 2 0 . 4 3 5 . 7 2 0 . 4 2 0 . 4 - 1 3 . 8 1 3 . 8 4 . 9 5 .4 5 . 5 1 2 . 9 1 4 . 4 1 4 . 2 6 .4 7 . 0 6 . 9 6 .2 7 . 0 7 . 0 2 5 . 6 2 8 . 5 2 8 . 2 8 . 5 1 2 . 0 1 1 . 8 9 . 1 1 3 . 2 1 3 . 2 1 7 . 7 2 5 . 3 2 5 . 1 - 1.6 1 .7 1.4 1 .8 1 .8 1 .6 2 . 5 2 . 5 Table 4.1 - Whole rock geochemical data for the Averill complex, including major, minor and trace element analyses and norm data. Numbered lithologies as in Figure 4.1. Note duplicate analyses of each sample to check for analytical precision. Error = S = standard deviation. fable 4.1 cont. Sample 8-1 8-2 182B-1 182B-2 AA-1 AA-2 635-1 635-2 Unit 3 3 3 3 3 3 3 3 S i 0 2 53.75 53.87 T i O , 0.58 0.56 A1 2 0 3 14.15 14.12 FeO 8.58 8.62 MnO 0.16 0.17 MgO 7.58 7.62 CaO 9.52 9.51 Na,0 3.34 3.31 K 2 0 2.88 2.79 P , 0 5 0.50 0.47 LOI 0.08 0.08 Tot 101.03 101.06 49. 86 48. 91 52. 45 1. 38 1. 36 0. 63 9. 70 9. 54 14. 75 14. 44 14. 51 8. 99 0. 00 0. 00 0. 18 5. 85 5. 74 7. 05 13. 57 13. 35 9. 11 1. 92 1. 86 3. 51 3. 77 3. 70 4 . 47 0. 96 0. 96 0. 60 0. 13 0. 13 0. 07 L01. 45 99. 92 101. 47 52. 43 50. 32 50. 66 0. 60 0. 69 0. 66 14. 55 15. 66 15. 01 8. 59 9. 36 9. 06 0. 18 0. 19 0. 19 6. 73 7. 65 7. 43 8. 65 10. 66 10. 15 3. 10 3. 77 3. 42 4. 22 2. 51 2. 38 0. 53 0. 59 0. 55 0. 07 0. 05 0. 05 99. 56 99. 50 101. 41 Ba 1302 1299 5014 4989 3216 3289 1615 1631 Cr 165 161 47 47 170 164 168 168 Nb 13 13 13 13 13 13 13 13 Ni 77 73 40 41 31 91 82 86 Rb 63 65 89 94 143 126 81 81 Sr 1404 1402 2976 3063 4030 3323 1736 1716 V 327 324 579 564 455 353 373 366 Y 19 17 51 53 36 19 19 22 Zr 43 44 228 227 195 136 62 61 OR 17.0 16.4 22.2 21.8 26.4 24.9 14.8 14.0 (AB) 24.6 25.4 2.7 2.3 8.0 13.5 10.2 15.7 (AN) 15.1 15.4 6.7 6.7 11.2 13.3 18.3 18.5 PL 39.7 40.9 9.4 9.1 19.3 26.8 28.6 34.3 NE 1.9 1.3 7.3 7.2 11.7 6.8 11.7 7.1 (WO) 12.0 11.9 22.6 22.2 14.2 12.6 14.5 13.4 (EN) 6.4 6.4 8.5 8.2 7.2 6.4 7.5 6.9 (FS) 5.1 5.1 14.4 14.3 6.6 5.9 6^5 6.1 Dl 23.6 23.5 45.7 44.8 28.1 24.9 28.6 26.5 (FO) 8.6 8.8 4.1 4.2 7.2 7.2 8.0 8.0 (FA) 7.6 7.7 7.7 8.0 7.3 7.3 7.8 7.7 OL 16.3 16.5 11.9 12.2 14.5 14.6 15.9 15.8 IL 1.1 1.0 2.6 2.5 1.2 1.1 1.3 1.2 AP 1.1 1.1 2.2 2.2 1.4 1.2 1.4 1.3 Table 4.1 cont. Sample 7-1 7-2 4-1-1 4-1-2 2-1 2-2 13-1 13-2 Unit 4 4 5 5 5 5 5 5 sio2 53. 63 53. 57 60. 55 60. 44 57. 18 57. 13 60. 66 60. 52 T i 0 2 0. 52 0. 52 0. 61 0. 59 0. 97 0. 97 0. 65 0. 65 A 1 2 0 3 14. 65 14. 63 17. 59 17. 67 14. 65 14. 66 17. 65 17. 83 FeO 8. 62 7 . 96 4. 63 4 . 57 7. 13 7. 14 5. 30 5. 22 MnO 0. 17 0. 17 0. 14 0. 14 0. 19 0. 19 0. 16 0. 16 MgO 7. 96 7 . 11 0. 78 0. 68 1. 85 1. 86 1. 01 0. 92 CaO 8. 21 8. 16 3. 75 3. 73 6. 19 6. 24 3. 96 3. 96 Na 20 3 . 28 3. 17 3. 41 3 . 54 2. 28 2. 39 3 . 95 3 . 92 K 2 0 3. 71 3. 72 8. 49 8. 50 8. 20 8. 17 8. 31 8. 27 P 205 0. 45 0. 42 0. 24 0. 21 0. 44 0. 43 0. 30 0. 29 LOI 0. 03 0. 03 0. 13 0. 13 0. 03 0. 03 0. 14 0. 14 Tot 99. 57 99. 42 100. 18 100. 08 99. 08 99. 19 101. 94 101. 72 Ba 1128 1183 2135 2104 3933 3947 2152 2096 Cr 169 163 16 13 17 17 13 11 Nb 13 13 13 13 13 13 13 13 Ni 77 73 16 10 15 17 8 9 Rb 63 130 130 239 190 186 180 185 Sr 1404 1114 1101 2499 4293 4196 3141 3197 V 270 274 167 172 286 265 187 178 Y 19 23 20 20 27 27 16 14 Zr 121 124 176 181 174 174 151 143 OR 16.4 21.9 50.1 50.2 48.4 48.2 49.1 48.8 (AB) 24.8 23.5 24.8 24.1 13.7 13.3 23.2 23.4 (AN) 15.4 14.7 7.6 7.2 5.5 5.1 5.8 6.6 PL 40.2 38.2 34.4 31.3 19.2 18.4 29.1 30.0 NE 1.7 1.7 2.1 3.1 3.0 3.7 5.5 5.2 (WO) 11.9 9.6 5.6 5.8 11.0 11.3 6.6 6.3 (EN) 6.3 5.1 1.1 1.1 3.1 3.2 1.5 1.3 (FS) 5.2 4.1 4.8 5.1 8.3 8.5 5.5 5.4 OI 23.5 18.9 11.6 12.1 22.5 23.1 13.6 13.1 (FO) 8.8 8.9 0.5 0.4 1.0 0.9 0.7 0.6 (FA) 7.9 7.8 2.4 2.1 2.9 2.7 2.8 2.8 OL 16.7 16.6 3.0 2.5 3.9 3.7 3.5 3.5 IL 1.0 0.9 1.1 1.1 1.8 1.8 1.2 1.2 AP 1.1 0.9 0.5 0.5 1.0 1.0 0 .7 0.6 58 Table 4.1 cont. Sample 4-2-2 4-2-1 6-1 6-2 9-1 9-2 Unit 5 5 6 6 7 7 SiO, 60. 88 60. 52 64. 00 64. 02 66. 24 66. 01 T i O , 0. 70 0. 70 0. 56 0. 57 0. 50 0. 50 A 1 2 0 3 16. 65 16. 67 18. 87 19. 05 16. 64 16. 63 Feo 5. 29 5. 27 3. 53 3. 52 3. 18 3. 24 MnO 0. 17 0. 16 0. 10 0. 10 0. 07 0. 07 MgO 0. 86 0. 91 0. 09 0. 03 1. 08 0. 94 CaO 4 . 77 4 . 77 0. 64 0. 65 3 . 71 3. 70 Na20 3 . 43 3. 46 5. 42 5. 59 4 . 00 4. 24 K 2 0 7. 85 7. 70 6. 67 6. 65 3. 18 3. 17 p 2 ° 5 0. 28 0. 28 0. 16 0. 16 0. 21 0. 21 LOI 0. 13 0. 13 0. 12 0. 12 0. 19 0. 19 Tot 100. 88 100. 44 100. 04 100. 33 98. 80 98. 69 Ba 2239 2195 574 582 1465 1508 Cr 13 11 37 42 17 21 Nb 13 13 13 13 13 13 Ni 14 15 12 12 6 10 Rb 187 189 297 297 98 99 Sr 3117 3133 426 429 1052 1077 V 198 189 2 2 72 82 Y 25 27 29 30 17 17 Zr 170 161 404 401 203 195 Q c OR (AB) (AN) PL NE (WO) (EN) (FS) Dl (EN) (FS) HY (FO) (FA) OL IL AP 0.0 45.5 27.0 7.2 34.3 1.1 7.8 1.6 6.6 16.1 0.0 0.0 0.0 0.4 1.8 2.3 1.3 0.6 0.0 46.3 26.8 6.8 33.7 1.1 7.9 1.6 6.9 16.4 0.0 0.0 0.0 0.3 1.7 2.1 1.3 0.6 1.3 0.4 39.4 45.8 6.2 52.0 0.0 0.0 0.0 0.0 0.2 6.0 6.2 1.0 0.3 0.5 0.3 39.3 47.3 6.2 53.5 0.0 0.0 0.0 0.0 0.0 6.0 6.0 1.0 0.3 18.2 18.7 33.8 18.0 51.9 1.2 0.4 0.8 2.5 2.2 4.5 6.8 0.0 0.0 0.0 0.9 0.5 17.0 18.7 35.8 16.9 52.8 1.7 0.5 1.2 3.4 1.8 4.3 6.1 0.0 0.0 0.0 0.9 0.5 59 4.7.3.2. Unit 5 For Unit 5 it was found that P is conserved during differentiation, and so the Pearce approach can be used to identify the minerals responsible for the differentiation trend (Russell and Nicholls, 1988). Figure 4.6 is a Pearce diagram which models the effect of plagioclase and alkali feldspar separation. The coefficients on the Y axis are chosen to mimic the stoichiometric relations found in natural feldspars between the cations Ca, Na and K and the X axis cations (Si or Al). Proper selection of the Y axis coefficients ensures that accumulation or removal of feldspar will cause a trend with a slope of 1 and a non zero intercept. In all the following Pearce diagrams a slope of 1 has been forced through an extreme composition. If the error bars for a data point intersect the forced slope, the data are said to lie along the slope. A zero intercept may indicate that the denominator constituent is not conserved (Russell and Nicholls, 1988). From Figure 4.6 it can be seen that syenites fall within error bars along a slope of 1. Therefore chemical variation between these rocks may be the result of the accumulation or removal of alkali and plagioclase feldspar. The trachyte dykes of Unit 6 do not fall along this trend. Figure 4.7 again models the effects of feldspar, using the same elements to mimic the stoichiometry of feldspars on the Y axis. The X axis cation is Si, relative to which the Y axis cations have a fixed stoichiometry. The same principles apply as for Figure 4.6. Again it can be seen that the syenites can be related through the loss or accumulation of feldspar, and that the trachyte dykes of Unit 6 cannot be explained solely by this mechanism. Any involvement of quartz would cause a slope shallower than 1, and if quartz alone had been involved in the differentiation process, the data would fall along a slope of 0. Figure 4.8 models the effects of alkali feldspar alone. The Y axis cations are chosen to mimic the stoichiometry of alkali feldspar, and Si is again plotted on the X axis. Rocks related by the accumulation or loss of alkali feldspar will fall along a slope of 1, with a non zero intercept. Any deviation from a slope of 1 indicates that alkali feldspar alone is not responsible for the variation in the data set. It can be seen from Figure 4.8 (2Ca+1Na+1K)/ 1P Figure 4.6 - Pearce element ratio diagram to model feldspar separation. Data are for Units 4, 5, and 6. Note that Sample 7 (Unit 4) is consistent with the data for Unit 5, indicating that Unit 4 can be related to Unit 5 by the accumulation or loss of feldspar. Note also that Unit 6 cannot be related to units 4 or 5 by this process. N*12. Error bars on all Pearce element ratio diagrams are calculated from XRF precision, and given as 2 std. deviations. o Figure 4.7 - Pearce element ratio diagram to model feldspar separation. Data are for Units 4, 5 and 6. Note that sample 7 (Unit 4) is consistent with the data for Unit 5, indicating that Unit 4 is related to Unit 5. Note also that Unit 6 cannot be related to Units 4 or 5 by this process. N = 12. (3Na+3K)/1P Figure 4.8 - Pearce element ratio diagram to model the effect of alkali feldspar, using P as a conserved element. Slope of 1 fits the data with a non-zero intercept indicating that the effect is almost entirely due to alkali feldspar. Data is for Units 5 and 6. N = 10. as to 63 that the syenites are related solely by the accumulation or loss of alkali feldspar. Rocks of Unit 6 also fall along this slope. Figure 4.9 is a similar test to model the effects of alkali feldspar. The Y axis is chosen to represent the stoichiometry of Al in alkali feldspar, and Si is again chosen for the X axis. Following the same principles used for Figures 4.6 to 4.8, it can be seen from Figure 4.9 that the data fall along a slope of 1 and are thus related solely by the accumulation or loss of alkali feldspar. The trachyte dykes are again consistent with this hypothesis, but they are not consistent with other figures (4.6, 4.7) therefore the hypothesis that they are related to Unit 5 through the fractionation of alkali feldspar must be rejected. It is possible that ferromagnesian minerals may also be partly responsible for the variation in the rock chemistry, and this can be tested by using a Pearce diagram that models the effects of ferromagnesian minerals. Figure 4.10 models the effects of Fe and Mg in olivine, with Si again used for the X axis. For example, if olivine were involved the data would fall along a slope of 1. It can be seen from Figure 4.10 that, within the error bars, the rocks create a scattered trend with no real variation along the Y axis. The involvement of any ferromagnesian phases would have resulted in some displacement parallel to the Y axis. Ferromagnesian phases are not involved in the differentiation history of these rocks, or participated trivially. It can therefore be concluded that the rocks of Unit 5 can be related through the crystallization of alkali feldspar alone. Figures 4.6 and 4.7, also contain data Unit 4 (samples 7-1 and 7-2). It can be seen from both of these figures that Unit 4 could be related to Unit 5 through the accumulation or loss of alkali feldspar. Sample 7 (monzonite) has almost the same chemistry as Sample 2 (syenite). Both have very low ratios of alkali feldspar components (Na, Ca and Al) to P as evidenced by their positions on Figures 4.6 and 4.7. The (Na, Ca, K)/P ratios increase from Sample 2 to Sample 4-1 (ie. along the slope of 1), which suggests that the 3AI/lf» 600 488 376 264 152. 4-1-1 IP An Si free 60 — i 1 1 1— 160 260 1 S J / 1 P 3 6 0 4 6 0 560 Figure 4.9 - Pearce element ratio diagram to model the effect of Al in feldspar, using P as a conserved element. The graph has a slope of 1 and a non-zero intercept, again indicating that the rocks can be related almost entirely by the removal of alkali feldspar. Data is for Units 5 and 6. N = 10. 4^ 1Fe+1Mg /1P 30H 1 1 1 H 40 146 252 1 S j j. 358 464 570 Figure 4.10 - Pearce element ratio diagram to model the effects of ferromagnesian minerals on differentiation. The data for Unit 5, within error bars, fit a slope of 0 indicating that ferromagnesian minerals are not involved in the differentiation process. Data for Unit 4 show that ferromagnesian minerals are involved, as expected, from petrography and geochemistry. N = 10. Ul 66 syenites are related by the accumulation, rather than the loss, of alkali feldspar. If it is true that Units 1 to 4 are related by simple crystal fractionation as suggested previously, the fact that Unit 4 can be related to Unit 5 suggests that all five of the plutonic rocks units are geochemically related. This implies that Units 1 to 5 represent a cogenetic suite of rocks. 4.7.3.3. Unit 6 For Unit 6 to be cogenetic with Unit 5 it would have to be consistent with the syenite data for every Pearce test. It can be seen from Figures 4.6, and 4.7 that the data for Unit 6 could not be related to Unit 5 by the accumulation or loss of plagioclase and alkali feldspar alone. Therefore other minerals are involved in their differentiation process for Unit 6. The trachytes are therefore not cogenetic with the syenites. 4.2. TRACE ELEMENTS Trace element analyses were obtained using X-ray fluorescence on a Phillips PW 1400 automated spectrometer in the Oceanography Dept. at the University of British Columbia. Pressed powder pellets were used and K-alpha peaks measured for each element. Counting times varied for each element, and in each case measurements were made for the peak, as well as the background counts below and above the peak (Oceanography Dept., UBC). 4.2.1. Trace element distribution Traditional variation diagrams illustrating the trace element concentration as a function of S i 0 2 content are shown in Figure 4.11. Continuous increases and decreases in concentration similar to those in the major elements are shown by Cr, Ni, Rb, V, and Y. Compatible elements Cr, Ni, V and Y all show a strong decrease in concentration with increasing S i 0 2 content, while the incompatible element Rb is the 6 7 3b E a a_ £ CL in P o C L 40 45 50 55 60 Si02 Wt.SB o • • • • 40 45 50 60 Si02 wt.SS Si02 wt.s? 65 70 35 40 45 50 55 60 Si02 wt.s 65 65 70 i i ; I I I I 35 40 45 50 55 60 65 70 70 35 40 45 50 55 60 Si02 Wt.SB CL E CL C L O J E CL do cr 65 CP o • o a • 70 35 40 45 50 55 60 65 70 Si02 Wt.SS 35 40 45 50 55 60 65 70 Si02 Wt.SS • a 35 40 45 50 55- 60 65 70 Si02 wt.56 Figure 4.11 - Harker diagrams showing the variation in trace elements with respect to silica. 68 only element that shows increased concentration. Ba, Sr and Zr concentrations show no correlation to S i 0 2 . The variation in Zr is very small and Ba and Sr both increase with increasing Rb content (Figure 4.12). Nb is at detection in all samples and thus has thus been excluded from Figure 4.11. Decreasing concentrations of Cr, Ni and V are consistent with the crystallizaton of clinopyroxene, hornblende and biotite (Gills, 1981; Deer, Howie and Zussman, 1983) and, as such, fits the proposed chemical model of removal of ferromagnesian minerals for Units 1 to 4. Increased concentration of Rb is consistent with the later crystallization of alkali feldspar syenites (Gill, 1981). Ba and Sr might also be expected to show increased concentrations as they too are contained in alkali feldspar, and Ba may also be present in biotite. Analyses of trace elements in alkali feldspars show Ba to be present in the alkali feldspar. Sr was always below detection. The general increases and decreases in concentration of the trace element data are therefore compatible with the variation in the major element geochemistry and are consistent with simple igneous differentiation for Unit 1 to 4. Trace element data for Units 6 and 7 are also shown on Figure 4.11. Both of these units plot as end members of the continuous variation trends. For most trace elements, Units 6 and 7 have similar concentrations. The greatest differences in their trace element chemistry are with respect to Rb and Zr. The Zr concentration of Unit 6 does not fit the trend defined by Units 1 to 5, of which Unit 7 appears to be an end member, and the Rb concentration of Unit 7 does not follow the continuous trend defined by Units 1 to 6. These observations are consistent with petrographic data and Pearce element ratio diagrams, which suggest that Units 6 and 7 are not cogenetic with Units 1 to 5. 2 5 0 3 0 0 Rb ppm o o _ o <X> j Q_ = L_ o • c / ) g : O 0 LTD CP • CD O CP S a I I 1 I I ! I I 5 0 1 1 1 1 1 1 1 1 1 1111 i 11 11 i i i i i II 11 i 1 1 1 1 1 1 111 I I • ' 100 1 5 0 2 0 0 Rb ppm 2 5 0 3 0 0 Figure 4.12 - Diagram to show the relative enrichment of Sr and Ba with respect to 70 4.2.2. Discrimination diagrams Trace element discrimination diagrams have been used by many authors (e.g. Pearce et al., 1984; Whalen et al., 1987) to determine tectonic affinities of various rock compositions. Although most of this work has been done for basalt (Erdman, 1985), the above authors have adapted plots that can be used for granitic rocks. Figure 4.13 (after Pearce et al., 1984) is used to discriminate between syn-collision, volcanic arc, within plate and normal and anomalous ocean ridge granites. From this Figure it can be seen that most of the rocks from the Averill suite have chemistry consistent with granitic rocks found in volcanic arcs. The notable exceptions to this classification are pyroxenites and one sample of the monzodiorite, which plot as orogenic and within plate granites respectively. This discrepancy arises from the attempt to classify ultramafic rocks in terms of the genesis of granitic rocks. The classification of these rocks as volcanic arc derived is consistent with regional tectonic models of southern British Columbia during the Tertiary (Armstrong, 1988; O'Brien et al., 1988). Also low Nb content, as in the Averill rocks has been suggested to be indicative of arc-type rocks (Gill, 1981). 4.3. CONCLUSIONS Rocks of the Averill alkaline plutonic complex are undersaturated with respect to silica, and have a very high Fe to Mg ratio. The only quartz normative rocks of tha Averill suite are the porphyry dykes of Unit 7, which are anomalous in terms of the rest of the suite. Compositionally the rocks are basic to intermediate. Variation in major element chemistry defines a progressive trend from mafic to felsic that is consistent with petrographic data, suggesting that the pyroxenites to monzonites are chemically related by loss of ferromagnesian minerals including augite, biotite and hornblende. This is also echoed in the trace element variation. AFM plots of the Averill data illustrate the high 71 1000 i S C G f WPG / ^ 1 0 0 --Q : cr : rjon VAG o / / ORG t i i i 11111 10 i i i Y 100 1 0 0 0 4- Nb Figure 4.13 - Tectonic discrimination diagram showing the arc-derived chemical trend of the Averill complex (after Pearce et al, 1984). ORG=ocean ridge granites; WPG=within plate granites; SCG=syn collision granites; VAG=volcanic arc granites. Lithology symbols as in Figure 4.1. 72 Fe/Mg signature of the rocks, and this is seen clearly when the Averill rocks are compared to other well known rock suites. Field, petrographic and geochemical observations of Units 1 to 4 provide a good basis to suggest that rocks of these units are related through simple igneous differentiation of augite, biotite and hornblende. Testing of petrologic hypotheses using Pearce element ratio diagrams has shown that Unit 4 is related to Unit 5 by the accumulation of alkali feldspar alone, and that all of the variation within Unit 5 can also be explained by this process. It is therefore probable that Units 1 to 5 are oogenetic. Unit 6, although having a similar chemistry to Unit 5, is not part of the oogenetic suite. Discrimination diagrams using trace element data suggest that the chemistry of Units 1 to 5 is consistent with formation in a volcanic arc regime. 73 5. PETROGENESIS 5.1. FIELD EVIDENCE Field exposures of contacts between units of the Averill plutonic complex are rare, and the majority of the boundaries on the geological map (Figure 1.4) are inferred. By far the best exposed lithologic contacts are the intrusive contacts between the syenite (Unit 5) and brecciated pyroxenites and monzogabbros (Units 1 and 2). These contacts are most commonly exposed in trenches and pits walls created during previous exploration efforts. The attitudes of these contacts have not been measured due to the poor nature of the contacts. Individual boulders show the style of brecciation affecting the more mafic lithologies (Plate 1). The presence of this brecciation suggests the relative age between the syenite (younger) and the pyroxenite (older). Precise details of the field relationships can be found in Chapter 2. Cross sections of the map area, showing only the orientation of the contacts at the surface are shown in Figure 1.5, and illustrate the zoned nature of the intrusion. Schematic sections extrapolated to depth, based solely on the nature of the surface contacts, are given in Figure 5.1. The sections illustrate possible contacts at depth, and thus show a postulated model of pluton emplacement.. 5.2. CHEMICAL VARIATION Geochemical data suggest that rocks of Unit 1 to 5 are genetically related. Major element chemistry for the rocks of the Averill complex shows a continuous variation between pyroxenite and syenite (Figure 4.1). This progressive evolution is also evident on other diagrams depicting major element variation (e.g. Figure 4.3). Testing of cogenetic hypotheses using Pearce element ratios has also shown that Units 4 and 5 are related. Furthermore, trace element data including Ni, Rb, V and Y also show smooth curvilinear trends from pyroxenite to syenite (Figure 4.11). The field relations, 5.1a Figure 5.1 - Inferred cross sections with contacts based on contact relationships seen at the surface. XX*=C-C';Y-Y' = B-B';Z-Z'=A-A'. Y S W 1300 1200 5 .1b 5 . 1 c 1400 1300 1200 1100 • 1000 900 800 700 77 petrography and geochemical data therefore argue that Units 1 to 5 represent a single petrographic suite (Carmichael, Turner and Verhoogen, 1977) and that the lithologic units may be related through igneous differentiation. Unit 5 represents the latest stage of evolution of the suite, and there is evidence to suggest that it is related to Unit 4 through accumulation of alkali feldspar. This is possible, as Unit 5 was intruded later than Units 1 to 4, and may thus have remained in a magma chamber where alkali feldspar accumulation could occur, during emplacement of the rest of the pluton. Trachyte dykes of Unit 6 cross cut Units 1 to 5, and are therefore the youngest intrusive unit. Petrographically Unit 6 is similar to Unit 5, comprising mainly alkali feldspar with interstitial mafic minerals. However, Unit 6 has been subjected to greater degrees of alteration and much of the primary mineralogy is no longer identifiable. Geochemically Unit 6 is again similar to Unit 5, but its differentiation history (Figure 4.6 to 4.9) cannot be explained in terms of alkali feldspar alone (as it can in Unit 5) suggesting that Unit 6 may not be oogenetic with Unit 5. Unit 7 is a suite of porphyry dykes which are dissimilar petrographically and geochemically to rocks of Units 1 to 6. They are the most siliceous rocks found in the Averill complex. Field evidence only suggests that they are coeval with the dykes of Unit 6. There are no grounds to presume that these rocks are related to any of the other rocks in the Averill complex. 5.3. SUMMARY Field, petrographic and geochemical data provide the basis of the petrogenetic model for the Averill complex, as shown in Figure 2.1. Units 1 to 4 were intruded as a single body, already partially differentiated at depth (see 4.1.1) which further differentiated after its intrusion. Differentiation of this body produced a zoned pluton with a mafic core (Unit 1) becoming more felsic to the outside (Unit 4). As this pluton was cooling, it was intruded by a late stage differentiate from the parent magma (Unit 5). This late stage material forcefully intruded through the base of the earlier formed zoned 78 pluton, brecciating the lower levels of the early pluton. The upper layers of the earlier pluton, still in the process of cooling during the intrusion of Unit 5, were not subjected to such forceful intrusion, and as a result the contacts between Unit 5 and Units 3 and 4 are of a gradational nature. Unit 5 crystallized with a slowly cooled, coarsely crystalline core component, and a mantle of much finer grained material. The entire complex has a north-west/south-east orientation, which is a common structural trend in southern British Columbia (Parrish et al., 1988). The two later dyke units, 6 and 7, follow a more north to north-north-east trend. Unit 6, although not cogenetic with Unit 5, has similar chemical affinities. Unit 7 is anomalous in terms of the rocks of the Averill complex. It is apparently coeval with Unit 6, sharing a common trend and never cutting or being cross cut by Unit 6. 79 6. IGNEOUS PROCESSES AND PLATINUM MINERALIZATION 6.1. FIELD EVIDENCE All visible mineralization in the Averill complex is associated in some way with crosscutting dykes or veins of syenitic material. Commonly, mineralization is visible within the syenitic dykes, concentrated along the margin of the dykes where they are in contact with the host rock. Less commonly mineralization may be found concentrated in pockets within the pyroxenite adjacent to syenite intrusions. Mineralization is weak, consisting mainly of copper-rich minerals the most common of which is chalcopyrite. Pyrite is less abundant and magnetite is occasionally present, tending to form cores of mineralized pockets. Malachite and hematite staining also occur. The host rocks for syenite dyke intrusion are usually Units 1 and 2, and occasionally Unit 3. Most of the mineralized exposure is found in pit rubble and in-situ outcrops containing mineralization are rare. The most extensive mineralization is found in the westernmost of the two structurally controlled outliers shown in Figure 2.2. At one locality in this outlier fragments of a syenitic pegmatite with abundant chalcopyrite were found. Analyzed sulphides from this pegmatite yielded 16 ppm platinum, with the major platinum mineral being sperrylite (Hulbert, pers.comm., 1988). 6.2. GEOCHEMICAL EVIDENCE Recent soil geochemical data found small platinum and palladium anomalies within the Averill complex. Platinum group element (PGE) values in the soil range from 10 to 45 ppb (Placer-Dome Inc., pers.comm.) and these values coincide with very much larger copper anomalies, which were always found to be associated with Unit 5 (Figure 6.1). It would seem therefore that the intrusion of Unit 5 may 80 Figure 6.1 - Distribution of soil geochemical platinum/palladium anomalies with respect to soil copper anomalies. 81 have initiated mineralization at the Averill Plutonic Complex, as most mineralization is found within or near dykes of Unit 5. Bulk sediment samples were collected from Franklin and Gloucester creeks and from the main body of Unit 1 (Fletcher, 1988). Concentrations of platinum and palladium in the soils range from 4 to 181 ppb, with the highest concentrations found in areas of friable, decomposing float of Unit 1 (Fletcher, 1988). Concentrations of platinum and palladium in the stream sediments range from 3 to 10 ppb (Fletcher, 1988). This suggests that PGE mineralization is present in the pyroxenite, although in low concentrations. Qualitative analyses of grains within the pyroxenite, using energy dispersive spectrometry (EDS) yielded no occurrences of PGE's. 6.3. COMPAR ISON TO OTHER PT BEARING BODIES Figures 6.2 to 6.4 compare the Averill plutonic complex to other platinum-bearing intrusions in Canada, using AFM diagrams. Rocks of the Tulameen complex in southern British Columbia (Findlay, 1969) show a greater range in composition than the rocks of the Averill complex. They tend to be higher in MgO and lower in FeO and alkalis relative to the Averill rocks. A similar comparison can be seen between the Averill rocks and those of the Lac des lies complex in Quebec. The Lac des lies trend (Pye, 1968) is considerably more enriched in MgO than is the Averill trend. The trend most similar to the Averill (from those shown) is that of the Onaping Formation of the Sudbury structure, Ontario. The rocks fall along the same general trend as those of the Averill, but are again enriched in Mg and depleted in Fe (Muir and Peredery, 1984) relative to the Averill rocks. All of these complexes have far greater platinum mineral potential than the Averill complex F i Figure 6.2 - Comparison of the Averil plutonic complex with the Tulameen ultramafic complex In Southern B.C.0=Averill sufte,rj=Tulameen suite. CD to Figure 6.3 - Comparison of the Averill plutonic complex with the Lac des lies ophiolite in Quebec. 0=Averi l l suite; •=Lac des lies suite. F 0 10 20 30 40 50 60 70 80 90 100 Figure 6.4 * Comparison of the Averill complex with the Onaping Formation of the Sudbufy ttjucture in Ontario, o = Averill; TJ= Sudbury. 03 85 (Pye, 1968; Findlay, 1969; Muir and Pereden/,1984), and the Sudbury structure is being actively mined for platinum (Muir and Peredery, 1984). 6.4. CONCLUSIONS The known facts regarding platinum/palladium mineralization at the Averill pluton are;-1) PGE mineralization is strongly associated with copper-rich mineralization; 2) copper-rich mineralization is strongly associated with the intrusion of Unit 5; and 3) PGE anomalies are most commonly associated with the contacts of Unit 5. The inference from these facts is that the magma generating Units 1 to 4 contained PGE's that were exploited during the intrusion of Unit 5. Platinum is a chalcophile element (Cabri, 1984) and as such would be expected to have an affinity to copper-rich minerals. A simple model for the generation of platinum mineralization is as follows. PGE's were present in the parent magma chamber. Platinum minerals, in the form of sperrylite (Thomlinson, 1920) crystallized with the intrusion and cooling of Units 1 to 4, being concentrated especially in Unit 1 (Thomlinson, 1920). PGE's remaining in the magma chamber were 'leached' out by the end-member syenitic magma. The greatest PGE concentrations are found where slow cooling allowed the formation of syenitic pegmatites. Elsewhere consequent cooling and crystallization resulted in copper-platinum rich sulphides, concentrated mainly along zones of contact between Units 1 and 5. 86 7.CONCLUS1QNS 1) Rocks of Units 1 to 4 of the Averill alkaline plutonic complex are related through the separation of augite, biotite, hornblende and, to a smaller extent, plagioclase feldspar (as plagioclase is present in Units 3 and 4 but not in Unit 5). This conclusion is based on field observations and petrography, and is supported by variations in both major and trace element geochemistry. 2) Rocks of Units 4 and 5 are related through the accumulation of alkali feldspar, as shown by Figures 4.11 and 4.12. Monzonites have chemical characteristics very similar to certain of the syenites, and the above mentioned figures indicate that the hypothesis that Unit 4 is related to Unit 5 through the accumulation of alkali feldspar cannot be rejected. Therefore, 3) rocks of Units 1 to 5 represent a oogenetic suite of alkaline plutonic rocks. Unit 5 thus represents the final stage of pluton differentiation. 4) Rocks of Units 6 and 7 are not part of this oogenetic suite. This is demonstrated by Figures 4.6,4.7, 4.11 and 4.12, where data for Unit 6 do .not fit the required slope of 1. Unit 7 is lithologically, petrographically and geochemically distinct from all of the other units, and as such cannot be inferred to be oogenetic with the rest of the suite. 5) The oogenetic suite comprising Units 1 to 5 may have been generated as part of a volcanic arc sequence. This is determined using trace element discrimination diagrams, and is consistent with tectonic models for southern British Columbia (Armstrong, 1988; O'Brien et al., 1988). 87 6) Platinum/palladium occurrences are associated with copper mineralization deriving from the intrusion of Unit 5. The mineralization is poor and extremely localized, and the resulting platinum mineralization is thus weak and uneconomic. 88 REFERENCES Armstrong, R. L, 1982. Cordilleran metamorphic core complexes - from Arizona to southern Canada. Annual Review of Earth and Planetary Sciences, 10,129-154. Armstrong, R.L, 1988. Mesozoic and early Cainozoic magmatic evolution of the Canadian Cordillera. Geological Society of America Special Paper 218 in S.P. Clark, B.C. Burchfiel and J.Suppe, Editors Process in continental lithosphere deformation: A symposium to honour John Rodjers, 55-91. Armstrong, R. L. Documentation for major and trace element reduction using UBCNET mainframe programs. University of British Columbia unpublished software. Baadsgaard, H., Folinsbee, R.E., Lipson, J . I., 1961. Potassium-argon dates of biotites from Cordilleran granites. Geological Society of America Bulletin, 72, 689-702. Bally, A.W., Gordy, P.L, Stewart, G.A., 1966. Structure, seismic data and orogenic evolution of the southern Canadian Rocky Mountains. Bulletin of Canadian Petroleum Geology, 14, 337-381. Bowen, N. L, 1928. The Evolution of the Igneous Rocks. Dover Publications, New York, 1958, 154p. Burchfiel, B.C., Davis, G.A., 1975. Nature and controls of Cordilleran orogenies, western United States. Extensions of an earlier synthesis. American Journal of Science, 275A, 363-396. Cabri, L. J . , 1984. Platinum-Group Elements: Mineralogy, Geology, Recovery. Canadian Institute of Mining and Metallurgy, Special volume 23,231 p. Cameca SX50 Reference Guide. 1st Edition, Cameca, France, 1988. Campbell, R.B., 1973. Structural cross-section and tectonic model of the southeastern Canadian Cordillera. Canadian Journal of Earth Science, 10,1607-1620. Carmichael, I. S. E., Turner, F. J . , and Verhoogen, J . , 1974. Igneous Petrology. McGraw-Hill, New York, 1974, 739p. Carmichael, I. S. E., 1964. The petrology of Thingmuli, a Tertiary volcano in eastern Iceland. Journal of Petrology, 5, 435-460. 89 Cheney, E.E., 1980. Kettle dome and related structures of northeastern Washington. Geological Society of America Memoir, 153, 463-484. Currie, K. L, 1976. The alkaline rocks of Canada. Geological Survey of Canada, Bulletin 239, 228p. Daly, R.A., 1912. Geology of the north American Cordillera at the 49th parallel. Geological Survey of Canada Memoir, 38, 857p. Drysdale, C.W., 1915. The geology of the Franklin mining camp, British Columbia. Geological Survey.of Canada Memoir, 56, 246p. Ecosoft, Inc., 1985. MICROSTAT - an interactive general purpose statistics package, release 4.1. Ecosoft, Indiana, 1985. Erdman, L. R., 1985. Chemistry of Neogene basalts of British Columbia and the adjacent Pacific ocean floor: A test of tectonic discrimination diagrams. MSc. thesis, University of British Columbia, Vancouver, unpublished, 294p. Ewing, T. E., 1981. Palaeogene tectonic evolution of the Pacific northwest. Journal of Geology, 88, 619-638. Findlay, D. C , 1969. Origin of the Tulameen ultramafic-gabbro complex, southern British Columbia. Canadian Journal of Earth Science, 6, 399p. Fletcher, W. K., 1988. Preliminary investigation of platinum content of soils ans sediments, southern British Columbia. Ministry of energy, Mines and Petroleum Resources, Paper 1989-1, 607-612. Gill, J . , 1981. Orogenic Andesites and Plate Tectonics. Springer-Verlag, New York, 1981, 390p. Griffiths, J.R., 1977. Mesozoic-early Cainozoic volcanism, plutonism and mineralization in southern British Columbia: A plate-tectonic synthesis. Canadian Journal of Earth Science, 14,1611 -1624. Hyndman, D. W., 1972. Petrology of the Igneous and Metamorphic Rocks. McGraw-Hill, New York, 1972, 533p. Keep, M., Russell. J.K., 1988. The geology of the Averill plutonic complex, Grand Forks, British Columbia; in Geological Fieldwork 1987, Department of Energy, Mines and Petroleum Resources Paper 88-1, 49-53. 90 Leroux, J . , 1980. Geothermal potential of the Coryell intrusions, Granby River area, British Columbia, in Current Research, Part B, Geological Survey of Canada Paper 80-1B, 213-215. Lisle, T.E., Chilcott, R.P., 1965. Report on Franklin mining camp, situated around Franklin mountain in the Greenwood Mining Division, province of British Columbia. Department of Mines and Petroleum Resources, Assessment Report 637, 30p. Little, H.W., 1957. Kettle River, east-half, British Columbia. Geological Survey of Canada, Map 6-1957. Little, H.W., 1961. Kettle River, west-half, British Columbia. Geological Survey of Canada, Map 15-1961. Little, H.W., 1962. Trail map-area, British Columbia. 82 F/4 east half. Geological Survey of Canada Paper 62-5, 7p. Little, H.W., 1963. Rossland map-area, British Columbia, 82 F/4 west half. Geological Survey of Canada Paper 63-13, 6p. Macdonald, G. A. and Katsura, T., 1964. Chemical composition of Hawaiian lavas. Journal of Petrology, 5, 82-133. Mader, U., Thirugnanam, U., and Russell, J . K., 1988. FORMULA-1: A Turbo-Pascal program for the calculation of mineral structural formulae. The University of British Columbia, unpublished U.B.C. software documentation, 40p. Mader, U., Kwong, S. D., and Russell, J . K., 1988. TRANSFORM - A Turbo-Pascal program to reduce electron microprobe data. University of British Columbia unpublished software. Miller, F.K., Engels, J . C , 1975. Distribution and trends of discordant ages of the plutonic rocks of northeastern Washington and northern Idaho. Geological Society of America Bulletin, 86, 517-528. Monger, J.W.H., Price, R. A., Tempelman-Kluit, D.J., 1982. Tectonic accretion and the origin of the two major metamorphic and plutonic welts in the Canadian Cordillera. Geology 10, 70-75. 91 Muir, T. L, and Peredery, W. V., 1984. The Onaping Formation. In The Geology and Ore Deposits of the Sudbury Structure, Edited by E.G. Pye, A.J. Naldrett and P.E. Giblin, Ontario Geological Survey Special Volume 1,139-210. Mutschler, F. E., Griffin, M. E., Scott Stevens, D., Shannon, S. S. Jr., 1985. Precious metal deposits related to alkaline rocks in the north American Cordillera - an interpretive review. Transactions of the Geological Society of South Africa, 88, 355-377. Nicholls, J . , and Stout, M. Z., 1988. Picritic melts in Kilauea - Evidence from the 1967-1968 Halemaumau and Hiiaka eruptions. Journal of Petrology, 29,1031-1057. Norman, G.W.H., 1969. Geological report on the Bear-Doe Group, Franklin district. Department of Mines and Petroleum Resources, Assessment report 1845, 6p. O'Brien, H. E., Irving, A. J . , and McCallum, I. S., 1988. The role of subduction in Eocene potassic magmatism of the Highwood Mountains, Montana. Geological Society of America, Abstracts with programs, 20, No.6, 46. Oceanography Department, University of British Columbia. Unpublished documentation for the analysis of trace elements by X-ray fluoresence. Parrish, R.R., Carr, S.D., Parkinson, D.L, 1988. Extensional tectonics of the southern Omineca belt, British Columbia and Washington. Tectonics, 7,181-212. Parrish R. R., and Carr, S. D., 1986. Extensional tectonics of southeastern British Columbia: new data and interpretation. Geological Association of Canada, Abstracts with programs, 11,112. Pearce, J . A., Harris, B. W., and Tindle, A. G., 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology, 25,956-983. Pearson, R .C , Obradovich, J.D., 1977. Eocene rocks in northeast Washington -radiometric ages and correlation. United States Geological Survey Bulletin, 1433,41 p. Pinsent, R.H., Cannon, R.W., 1988. Geological, geochemical and geophysical assessment report, Platinum Blonde property, Franklin Creek area, Greenwood Mining Division, British Columbia. Department of Energy, Mines and Petroleum Resources, Assessment Report, 248p. Price, R.A., 1981. The Cordilleran foreland thrust and fold belt in the southern Canadian Rocky Mountains, in K.R. McClay and N.J. Price (eds.) Thrust and Nappe Tectonics, 1981, Geological Society of London Special Publication 9, 427-448. 92 Price, R. A., 1985. Metamorphic core complexes of the first and second kind in the Cordillera of southern Canada and northern U.S.A. Geological Society of America, Abstracts with programs, 17, 401. Price, R. A., Monger, J . W. H., and Roddick, J . A., 1985. Cordilleran cross section -Calgary to Vancouver: in Field Guides to Geology and Mineral Deposits in the southern Canadian Cordillera. Geological Society of America, Cordilleran section, 3-1 to 3-83. Pye, E. G., 1968. Geology of the Lac des lies area. Ontario Geological Survey Geological Report 64, 47p. Rebagliati, M., 1989. The Mt. Milligan alkaline Au-Cu porphyry deposit, north central British Columbia. Geological Association of Canada Mineral Deposits Division, Au-Cu Porphyry Short Course, unpublished notes. Rublee, J . , 1986. Occurrence and distribution of platinum group elements in British Columbia. British Columbia Department of Energy, Mines and Petroleum Resources, Open-file 1986-7, 94p. Russell, J . K., and Nicholls, J . , 1988. Analysis of petrologic hypotheses with Pearce element ratios. Contributions to Mineralogy and Petrology, 99, 25-35. Russell, J . K., Horsky, S., Thirugnanam, U., 1988. XRF3 - Users Guide and Documentation. University of British Columbia unpublished software. Streckeisen, A, 1975. To each plutonic rock its proper name. Earth-Science Review, 12, 1-33. Thomlinson, W. V., 1920. Platinum mineral investigations. Munitions Resource Commission, Canada, Final Report, 161-166. Whalen, J . B., Currie, K. L, and Chappell, B. W., 1987. A-type granites: geochemical characteristics, discrimination and petrogenesis. Contributions to Mineralogy and Petrology, 95, 407-419. 93 APPENDIX A. E LECTRON MICROPROBE ANALYSES Appendix A contains details of data reduction techniques and gives tabulated analyses representative of each mineral phase in each unit. Details of electron microprobe operating and analytical conditions, as well as information on the standards are given in detail at the beginning of Chapter 3. 94 Data reduction techniques Raw data from the electron microprobe was initially reduced using the computer program TRANSFORM (Mader et al, 1988) which was developed specifically to transform the raw data (element or oxide weight per cent)to the correct format for further reduction using program FORMULA 1 (Thirugnanam et al, 1988). This program has been developed at the University of British Columbia to calculate mineral structural formulae. The program can be modified to incorporate any mineral group, and specific cases of mineral stoichiometry. Mineral structural formulae can be calculated by having either a fixed anion sum, or where possible, a fixed cation sum. Errors for each element were calculated using the program MICROSTAT (Ecosoft, Inc., 1985), a statistics package which allows the calculation of a variety of statistical tests. The precision estimates given are those from the standards, which were analysed several times each during the duration of microprobe analyses. The following analyses are those representing the range of composition of each mineral phase in each rock Unit and are discussed in Chapter 3. Estimates of precision are given as one standard deviation. PYROXENE ELECTRON MICROPPROBE ANALYSES Sample A l l A l l 11 11 10-2 10-2 10-1 10-1 8 8 8 U n i t 1 1 1 1 2 2 2 2 3 3 3 Type MG FE MG FE FE MG MG FE CA MG FE S i 02 52. 47 45. 81 48. 34 48. 04 49. 99 52. 79 51. 08 48. 78 53. 55 51. 23 50. 54 0. 265 T i 02 0. 23 0. 83 0. 69 0. 53 0. 33 0. 13 0. 14 0. 40 0. 05 0. 42 0. 50 0. 033 A l o O o 0. 82 6. 21 4. 31 4. 35 3. 92 1. 59 2. 65 5. 12 0. 64 4. 18 5. 82 0. 047 FeO 7. 30 13. 93 11. 74 15. 45 9. 77 8. 27 9. 22 10. 59 7. 17 10. 26 13. 48 0. 521 MnO 0. 35 0. 43 0. 50 0. 60 0. 47 0. 49 0. 35 0. 34 0. 42 0. 33 0. 36 0. 053 MgO 14. 28 11. 56 10. 29 7. 79 12. 24 14. 00 13. 45 11. 30 14. 77 15. 15 15. 45 0. 088 CaO 23. 68 17. 08 22. 58 20. 81 22. 75 23. 25 22. 26 23 . 12 23. 55 16. 98 11. 68 0. 176 Na20 0. 77 1. 83 0. 98 1. 80 0. 77 0. 55 0. 54 0. 68 0. 37 0. 68 0. 97 0. 056 Tot 99. 90 98. 35 99. 43 99. 37 100. 25 101. 08 99. 70 100. 33 100. 53 99. 25 98. 80 s i 1.94 1.73 1.83 1.84 1.88 1.95 1.92 1. 84 1.98 1.91 1.89 T i 0.01 0.02 0.02 0.02 0.01 0.00 0.00 0. 01 0.00 0.01 0.01 A l 0.04 0.28 0.19 0.20 0. 17 0.07 0.12 0.23 0.03 0.18 0.26 Fe 0.23 0.44 0.37 0.50 0.31 0.26 0.29 0.33 0.22 0.32 0.42 Mn 0.01 0.01 0.02 0.02 0.01 0.02 0.01 0. 01 0.01 0.01 0.01 Mg 0.79 0.65 0.58 0.44 0.69 0.77 0.75 0.64 0.81 0.84 0.86 Ca 0.94 0.69 0.92 0.85 0.92 0.92 0.90 0.94 0.93 0. 68 0.47 Na 0. 06 0.13 0.07 0.13 0.06 0. 04 0.04 0. 05 0. 03 0. 05 0. 07 0 5.94 5.81 5.91 5.89 6.00 6.00 6.00 6. 00 6.00 6. 00 6.00 Tot 9.94 9.81 9.91 9.89 10.05 10.03 10. 04 10. 05 10.02 10. 01 10.00 PYROXENE ELECTRON MICROPROBE ANALYSES - CONT. Sample U n i t Type AA AA 635 635 7 7 13 13 13 4-2 4-2 3 3 3 3 4 4 5 5 5 5 5 FE MG FE MG CA/FE MG MG FE CA MG FE S i 02 50.43 52.19 T i 02 0.46 0.24 A1203 3.06 2.51 FeO 12.44 7.28 MnO 0.42 0.32 MgO 10.43 14.17 CaO 21.09 23.04 Na20 1.77 0.77 Tot 100.10 100.51 51. 62 51. 43 37. 64 0. 09 0. 09 1. 49 1. 18 0. 81 22. 77 8. 37 6. 77 12. 60 0. 54 0. 42 0. 05 14. 85 15. 44 0. 08 22. 59 22. 69 23. 64 0. 51 0. 46 0. 01 99. 76 98. 14 98. 29 54. 91 53. 43 50. 48 0. 03 0. 01 0. 13 1. 76 0. 85 2. 70 11. 04 12. 91 16. 51 0. 50 0. 75 0. 67 18. 09 10. 14 8. 03 11. 47 17. 85 18. 88 0. 48 3. 94 3 . 08 98. 28 99. 87 100. 47 50. 54 52 . 75 52. 65 0. 09 0. 02 0. 00 2. 63 0. 80 1. 65 15. 75 13 . 85 15. 58 0. 68 0. 65 0. 57 8 . 33 10. 46 8. 94 19. 52 17 . 83 17. 50 2. 81 3 . 74 4 . 06 100.36 99.71 100.95 S i 1.89 1.92 1.91 1.93 1.47 T i 0.01 0.01 0.00 0.00 0.04 A l 0.14 0.11 0.05 0.04 1.05 Fe 0.39 0.22 0.26 0.21 0.41 Mn 0.01 0.01 0.02 0.01 0. 00 Mg 0.58 0.78 0.82 0. 86 0. 00 Ca 0.85 0.91 0.90 0.91 0.99 Na 0.13 0.05 0.04 0. 03 0. 00 0 5.91 5.95 5.92 5.93 6.00 Tot 9.91 9.95 9.92 9.93 9.97 2. 03 1. 98 1. 90 1. 90 1. 96 1. 95 0. 00 0. 00 0. 00 0. 00 0. 00 0. 00 0. 08 0. 04 0. 12 0. 12 0. 04 0. 07 0. 34 0. 40 0. 52 0. 50 0. 42 0. 48 0. 02 0. 02 0. 02 0. 02 0. 02 0. 02 1. 00 0. 56 0. 45 0. 47 0. 58 0. 49 0. 45 0. 71 0. 76 0. 79 0. 71 0. 69 0. 03 0. 28 0. 22 0. 21 0. 27 0. 29 6. 00 5. 86 5. 85 5. 86 5. 85 5. 84 9. 95 9. 86 9. 85 9. 86 9. 85 9. 84 PYROXENE ELECTRON MICROPROBE ANALYSES - CONT. Sample 4-2 U n i t 5 Type CA 4-1 4-1 4-1 2 2 2 5 5 5 5 5 5 FE CA MG MG CA FE Si02 52.83 Ti02 0.00 A1203 1.02 FeO 13.62 MnO 0.60 MgO 10.12 CaO 18.72 Na20 3.45 Tot 100.37 49.51 49.47 0.35 0.33 2.93 2.95 17.03 17.01 0.61 0.57 7.36 7.29 19.82 20.20 2.23 2.23 99.84 100.05 51.20 51.61 0.14 0.09 2.34 2.31 15.53 13.38 0.67 0.51 8.71 9.84 19.73 20.30 2.73 2.35 101.05 100.39 46.42 47.30 0.62 0.65 4.42 4.28 16.42 17.24 0.67 0.71 7.24 7.33 21.59 21.29 1.46 1.39 98.87 100.21 S i 1.96 T i 0.00 A l 0.04 Fe 0.42 Mn 0.02 Mg 0.56 Ca 0.74 Na 0.25 O 5.86 Tot 9.86 1. 89 1. 89 0. 01 0. 01 0. 13 0. 13 0. 55 0. 54 0. 02 0. 02 0. 42 0. 42 0. 81 0. 83 0. 17 0. 16 5. 89 5. 88 9. 89 9. 88 1. 91 1. 93 0. 00 0. 00 0. 10 0. 10 0. 49 0. 42 0. 02 0. 02 0. 49 0. 55 0. 79 0. 81 0. 20 0. 17 5. 87 5. 90 9. 87 9. 90 1. 80 1. 81 0. 02 0. 02 0. 20 0. 19 0. 53 0. 55 0. 02 0. 02 0. 42 0. 42 0. 90 0. 87 0. 11 0. 10 5. 87 5. 88 9. 87 9. 88 FELDSPAR ELECTRON MICROPROBE ANALYSES Sample 11 11 10-2 10-2 10-2 10-1 10-1 8 8 8 U n i t 1 1 2 2 2 2 2 3 3 3 Type Na K K Na Ca Na K Ca Na K S i 30. 40 29. 30 29. 76 31. 65 30. 35 28. 95 24. 26 26. 95 28. 43 29. 86 0. 535 A l 10. 59 10. 14 9. 83 10. 52 10. 17 11. 26 16. 45 14 . 07 13. 17 10. 00 0. 126 Ca 0. 25 0. 12 0. 01 0. 18 0. 34 3. 04 0. 39 5. 97 4. 13 0. 00 0. 066 Na 5. 13 0. 98 0. 44 8. 63 2. 93 6. 90 2. 28 5. 13 6. 14 0. 65 0. 010 K 5. 42 12. 57 13. 64 0. 06 9. 57 0. 16 7. 30 0. 08 0. 31 13. 03 0. 081 Ba 1. 03 1. 06 0. 13 0. 00 0. 16 0. 09 0. 71 0. 18 0. 12 1. 92 0. 143 0 47. 18 45. 53 45. 65 48. 55 46. 78 47. 03 45. 42 47 . 44 47 . 99 46. 04 Tot 100. 00 99. 70 99. 46 99. 59 100. 30 97. 43 96. 81 99. 74 100. 29 101. 50 S i 2.94 2.93 2.97 A l 1.06 1.06 1.02 Ca 0.02 0.01 0.00 Na 0.61 0. 12 0.05 K 0.38 0.90 0.98 Ba 0.02 0. 02 0.00 0 8.00 8. 00 8.00 Tot 13.03 13.04 13.02 2.97 2.96 2.81 2.43 1.03 1.03 1.14 1.72 0.01 0.02 0.21 0.03 0.99 0.35 0.82 0.28 0.00 0.67 0.01 0. 53 0.00 0.00 0.00 0.01 8.00 8.00 8.00 8.00 13.00 13.03 12.99 13.00 2. 60 2. 59 2. 70 2. 96 0. 08 1. 41 1. 30 1. 03 1. 32 0. 40 0. 27 0. 00 0. 05 0. 60 0. 71 0. 65 0. 00 0. 01 0. 02 0. 93 0. 00 0. 00 0. 00 0. 04 8. 00 8. 00 8. 00 8. 00 .2 . 05 13 . 01 13. 00 13 . 03 FELDSPAR ELECTRON MICROPROBE ANALYSES - CONT. Sample 635 635 AA AA U n i t 3 3 3 3 Type Na K K Na 7 7 13 13 4-2 4-2 4 4 5 5 5 5 K Na K Na Na K S i 30. 68 26. 15 25. 76 26. 25 29. 58 32. 20 29. 59 29. 96 29. 53 29. 88 A l 11. 25 15. 22 14. 83 14. 72 9. 96 10. 59 9. 92 9. 99 9. 79 9. 83 Ca 1. 13 0. 42 7. 42 6. 86 0. 00 0. 05 0. 01 0. 10 0. 00 0. 00 Na 7. 53 4. 24 4. 29 4. 62 0. 35 8. 73 0. 40 1. 98 1. 12 0. 47 K 0. 28 5. 11 0. 04 0. 05 13. 60 0. 05 13. 67 10. 95 11. 70 13. 70 Ba 0. 00 0. 03 0. 07 0. 03 1. 54 0. 06 0. 21 0. 43 0. 85 1. 64 0 48. 16 46. 24 47. 04 47. 41 45. 66 49. 31 45. 51 46. 08 45. 26 45. 82 Tot 99. 03 97. 41 99. 45 99. 94 100. 69 100. 99 99. 31 99. 49 98. 25 101. 34 S i 2.90 2.58 2.50 2.52 2.95 2.99 2.96 2 .96 2.97 2.97 A l 1.11 1.56 1.50 1.47 1.03 1.02 1. 03 1.03 1. 03 1.02 Ca 0.08 0.03 0.50 0.46 0.00 0.00 0.00 0. 01 0.00 0. 00 Na 0.87 0.51 0.51 0.54 0.04 0.99 0. 05 0.24 0. 14 0.06 K 0.02 0.36 0.00 0.00 0.98 0.00 0.98 0.78 0.85 0.98 Ba 0.00 0.00 0.00 0.00 0.03 0.00 0.00 0. 01 0. 02 0. 01 O 8.00 8.00 8.00 8.00 8.00 8.00 8.00 8.00 8.00 8.00 Tot 12.98 13.04 13.01 12.99 13.03 13.00 13.02 13.03 13. 01 13.04 VO VO F E L D S P A R E L E C T R O N MICROPROBE A N A L Y S E S - C O N T . Sample 4-1 4-1 2 2 U n i t 5 5 5 5 Type Na K K Na S i 30. 05 30. 06 29. 49 29. 42 A l 9. 90 9. 95 10. 01 9. 80 Ca 0. 05 0. 00 0. 02 0. 10 Na 2. 10 0. 43 0. 52 1. 35 K 10. 85 13. 60 13. 39 11. 75 Ba 0. 25 0. 19 0. 70 0. 73 0 46. 07 46. 08 45. 52 45. 27 Tot 99. 27 100. 31 99. 65 98. 42 S i 2.97 2.97 2.58 2.95 A l 1. 02 1.02 0.09 1.04 Ca 0. 00 0.00 1.31 0.00 Na 0.25 0. 05 0.04 0.06 K 0.77 0.97 0.00 0.96 Ba 0.01 0.00 0.01 0.01 O 8. 00 8. 00 8.00 8.00 Tot 13.02 13.01 12.03 13.02 G A R N E T E L E C T R O N M I C R O P R O B E A N A L Y S E S Sample 13 4-2 4-1 2 s Unit 5 5 5 5 Type Av Av Av Av S i 02 34.57 34.87 T i 02 1.88 1.44 A l g 03 4.23 3.42 F e203 28.32 29.61 MnO 0.76 0.68 MgO 0.20 0.14 CaO 31.88 32.33 Tot 101.84 102.53 33. 63 34. 63 0. 265 2. 09 1. 98 0. 033 3. 27 3. 85 0. 047 31. 11 29. 32 0. 521 0. 72 0. 71 0. 053 0. 20 0. 25 0. 088 31. 65 31. 81 0. 176 102.70 102.61 S i 2.84 2.85 2.76 2. 83 T i 0.12 0.09 0.13 0. 12 A l 0.41 0.33 0.32 0. 37 Fe3 1.75 1.82 1.92 1. 80 Mn 0.05 0.05 0.05 0. 05 Mg 0.02 0.02 0.02 0. 03 Ca 2.81 2.84 2.79 2. 79 O 12.04 12.02 12.02 12. 04 Tot 20.04 20.02 20.02 20. 04 B I O T I T E E L E C T R O N MICROPROBE A N A L Y S E S Sample A l l 10-2 10-1 635 AA 8 4-2 U n i t 1 2 2 3 3 3 5 Type Av AV AV AV AV Av Av S i 16. 49 16. 98 16. 86 17. 22 17. 00 17. 64 17. 70 0. 458 T i 1. 24 1. 38 0. 88 1. 40 1. 32 1. 26 0. 54 0. 006 A l 7. 82 8. 23 8. 70 7. 79 7. 73 7. 52 7. 15 0. 359 Fe 14. 98 14. 00 12. 67 12. 93 14. 29 12. 99 14. 31 0. 412 Mn 0. 34 0. 27 0. 28 0. 21 0. 16 0. 16 0. 46 0. 036 Mg 8. 09 8. 28 8. 88 8. 76 8. 20 8 . 59 8. 79 0. 534 Na 0. 21 0. 09 0. 14 0. 06 0. 11 0. 08 0. 05 0. 025 K 7. 46 7. 55 7. 73 7. 58 7. 57 7. 80 7. 10 0. 721 F 0. 92 0. 16 0. 37 0. 21 0. 99 0. 19 1. 17 0. 106 C l 0. 02 0. 08 0. 06 0. 14 0. 01 0. 13 0. 01 0. 014 0 38. 28 38. 79 38. 89 38. 71 38. 67 38. 79 38. 87 Tot 95. 85 95. 02 95. 47 95. 02 96. 05 95. 16 96. 17 S i 5.49 T i 0.24 A l 2.71 Fe 2.51 Mn 0.06 Mg 3.12 Na 0.09 K 1.78 F 0.45 C l 0.00 O 22.15 Tot 38.61 5.58 5.51 0.27 0.17 2.82 2.96 2.32 2.08 0.05 0.05 3.14 3.35 0.04 0.05 1.78 1.82 0.08 0.18 0.02 0.01 22.35 22.23 38.44 38.42 5. 69 5. 65 0. 27 0. 26 2. 68 2. 67 2. 15 2. 39 0. 04 0. 03 3. 34 3. 15 0. 02 0. 05 1. 80 1. 81 0. 10 0. 49 0. 04 0. 00 22. 39 22. 32 38. 53 38. 81 5. 82 5. 87 0. 24 0. 10 2 . 59 2. 47 2. 16 2. 39 0. 03 0. 08 3. 28 3. 37 0. 03 0. 02 1. 85 1. 69 0. 09 0. 58 0. 04 0. 00 22. 42 22. 36 38. 55 38. 93 HORNBLENDE ELECTRON MICROPROBE ANALYSES Sample A l l 10-1 AA U n i t 1 2 3 Type Av Av Av 8 7 4-2 2 s 3 4 5 5 AV Av Av Av S i 17.99 17. 91 18. 73 22. 21 23. 50 18. 27 18. 07 0. 458 T i 0.94 0. 78 0. 44 0. 43 0. 00 0. 60 0. 45 0. 006 A l 6.54 7. 31 6. 23 3. 57 2. 76 6. 00 6. 34 0. 359 Fe 17.10 15. 03 14. 65 10. 67 11. 21 18. 03 17. 39 0. 412 Mn 0.45 0. 28 0. 36 0. 27 0. 37 0. 63 0. 56 0. 036 Mg 4.26 5. 57 5. 92 8. 57 8. 77 4. 08 4. 46 0. 534 Ca 8.09 8. 50 7. 99 8. 69 8. 22 7. 92 8. 04 0. 010 Na 2.06 1. 56 2. 46 0. 88 0. 85 1. 99 1. 82 0. 025 K 1.62 1. 86 1. 45 0. 53 0. 34 1. 77 1. 80 0. 721 F 0.44 0. 19 0. 69 0. 08 0. 11 0. 48 0. 43 0. 106 C l 0.06 0. 07 0. 04 0. 06 0. 06 0. 05 0. 07 0. 014 0 39.26 39. 89 40. 02 41. 48 42. 03 39. 02 39. 02 Tot 98.82 98. 96 98. 98 97. 45 98. 22 98. 85 98. 45 S i 6.23 T i 0.19 A l 2.36 Fe 2.98 Mn 0.08 Mg 1.71 Ca 1.96 Na 0.87 K 0.40 F 0.23 C l 0.02 0 23.76 Tot 40.79 6. 12 6. 35 0. 16 0. 09 2. 60 2. 20 2. 58 2. 50 0. 05 0. 06 2. 20 2. 32 2. 04 1. 90 0. 65 1. 02 0. 46 0. 35 0. 10 0. 34 0. 02 0. 01 23. 88 23. 65 40. 86 40. 79 7. 47 7. 63 0. 07 0. 00 1. 06 0. 93 1. 69 1. 83 0. 05 0. 06 3. 22 3. 29 2. 11 1. 87 0. 31 0. 34 0. 10 0. 08 0. 05 0. 06 0. 01 0. 02 23. 94 23. 93 40. 08 40. 04 6. 37 6. 30 0. 12 0. 09 2. 18 2. 30 3. 16 3 . 05 0. 11 0. 10 1. 64 1. 80 1. 94 1. 96 0. 85 0. 78 0. 44 0. 45 0. 25 0. 22 0. 01 0. 02 23. 74 23. 76 40. 81 40. 83 A P A T I T E E L E C T R O N MICROPROBE A N A L Y S E S Sample A l l U n i t 1 Type Av 11 10-2 10-1 8 635 7 13 4-2 4-1 2 1 2 2 3 3 4 5 5 5 5 AV Av Av Av Av AV Av Av AV Av S i Ca P F 0 0.47 0.43 0.29 0.32 40.22 39.04 39.05 39.23 39.09 39.30 38.75 39.16 38.74 37.75 38.14 17.39 17.44 17.33 17.48 18.16 18.33 17.86 17.42 17.35 16.31 18.23 4.03 5.47 5.56 4.77 3.51 3.80 4.47 6.25 6.45 6.38 4.96 40.32 40.66 40.59 40.57 40.65 41.09 40.78 41.30 41.10 39.16 41.24 0.146 0.357 0.616 0.324 Tot 101.96 102.61 102.53 102.05 101.41 102.52 101.85 104.59 104.06 99.89 102.88 S i - -Ca 5.13 5.07 P 2.87 2.93 F 1.08 1.50 0 12.34 12.48 Tot 21.42 21.97 5.08 5.07 5.00 2.92 2.93 3.00 1.53 1.30 0.95 12.47 12.50 21.49 21.99 21.80 21.49 0.08 4.99 5.01 5.02 3.01 2.99 2.89 1.02 1.25 1.69 12.56 12.53 12.42 21.57 21.78 22.11 0.07 0.05 0.05 5.01 5.09 4.90 2.90 2.84 3.03 1.76 1.81 1.34 12.44 12.33 12.61 22.20 22.14 21.96 H O S P H E N E E L E C T R O N M I C R O P R O B E A N A L Y S E S Sample 13 4-1 4-2 2 U n i t 5 5 5 5 Type Av AV AV AV Si 14. 71 14. 55 14.43 14. 54 0. 243 T i 20. 03 21. 12 21.48 21. 12 0. 826 Al 1. 00 0. 88 0.72 0. 71 0. 141 Fe 1. 46 1. 65 1.38 1. 47 0. 310 Ca 20. 11 20. 24 20.21 20. 09 0. 656 Na 0. 02 0. 05 0.04 0. 04 0. 080 o 39. 82 40. 50 40.33 40. 13 Tot 97. 15 99. 01 98.59 98. 12 Si 1.04 1.02 1.01 1.03 T i 0.83 0.87 0.89 0.87 Al 0.07 0.06 0.05 0.05 Fe 0.05 0.06 0.05 0. 05 Ca 1.00 0.99 1.00 0.99 Na 0.00 0.00 0.00 0.00 0 4.95 4.97 4.98 4.97 Tot 7.95 7.97 7.98 7.97 106 APPENDIX B. WHOLE ROCK MAJOR AND TRACE ELEMENT ANALYSES Appendix B gives details of sample preparation, data aquisition and reduction techniques used for whole rock chemical analyses. Whole rock major and trace element analyses and CIPW norms for all of the rocks of the Averill complex are given in Table 4.1. A sample location map showing the location of all of the samples used for major and trace element analyses is given in Figure A.1. The samples are the same as those used for electron microprobe analysis. 107 Loss on ignition Prior to LOI determination, porcelain crucibles are thoroughly washed, rinsed in deionized-ionized water and left to dry in an oven at 120°c for 30 minutes. Each crucible is subsequently weighed to four decimal places, and the weight recorded. Approximately one gramme of rock powder is added to the crucible, and the combined weight of the crucible and powder is precisely recorded. The crucibles plus powder are left for eight hours or overnight in an oven at 120°C, and then weighed again to determine the value of H2O". After weighing, the samples are then transferred to an oven at 750°C for eight hours or overnight. On removal the samples are weighed a final time to determine the loss on ignition. At all times when the samples are not in an oven or being weighed , they are kept in a dessicator. The precision achieved during this process was calculated by determining the loss on ignition of a single sample 6 times. It was found that 1 standard deviation on the sample was 0.016. Precision estimates for LOI were calculated using the computer program MICROSTAT (Ecosoft Systems Inc.) PELLET PREPARATION Both crushed fused glass and pressed powder pellets were made. Crushed fused glass pellets were used for major element analyses, while pressed powder pellets were used for trace element analyses. First, loss on ignition was measured on 1 gram of rock powder. Next, 1 gram of dehydrated rock powder was mixed with 2 grams of lithium tetraborate, and fused for ten minutes at 1000°C. The resulting fused button was then crushed and a pressed glass powder pellet prepared. Glass powder was mixed with two or three drops of polyvinylalcohol to improve binding, and the mixture was covered with boric acid and pressed for 1 minute at a force equivalent to 20 tonnes in a stainless steel die apparatus. 108 DATA ACQUISITION K-alpha peaks were measured for all elements, and a monitor (BCR-1) was run in every fourth position to check for drift in the machine. Peak counts were collected for ten seconds on all elements, except for P, Mg, Na and Mn, which were analysed for 100 seconds each. Background counts were measured for 10 seconds n each element. Data reduction Major element analysis was performed on the crushed fused glass pellets described above, while trace element analysis was peformed on pressed powder pellets. Duplicate pellets were made for all samples to check the precision of the sample preparation. Precision was estimated from repeated analyses on the monitor. All of the standards used were USGS rock powders. The major element data was reduced using the program XRF3 (Russell et al, 1988), developed at the University of British Columbia. This program takes raw data (counts) and calculates weight percentages of major elements. The program also calculates peak and background counts per second, corrected counts per second, as well as statistics for the monitor, and also produces calibration curves for the standards. Trace element data were reduced using mainframe programs MAC.R (to calculate mass absorption coefficients) and CALIB.O (to calculate concentrations of trace elements) on the University of British Columbia UBCNET system (Armstrong, unpublished). CIPW norms were calculated using the UBCNET program ROCK. Figure A.1 - Sample location map for ail of the samples used in EMP and XRF analysis. APPENDIX C. GEOCHRONOLOGY During the course of this study, a potassium argon age date was obtained from a sample of pyroxenite. The sample was dated at 150 +/- 5 Ma (U.B.C. Geochronology Lab, unpublished data). The pyroxenite was collected from 118°23'45"E, 49°35'25"N (see Figure 1.3), at the base of a scree slope of pyroxenite. The age of the unit was previously thought to be part of the Eocene Coryell intrusives, and was constrained to be post-Middle Jurassic to pre-Lower Eocene by its relationships to other known rocks. The material analyzed for the K-Ar date was a separate including augite, hornblende and biotite. The Jurassic age determined for the pyroxenite of the Averill complex is significant in terms of regional tectonic interpretations. There are several other Jurassic alkali bodies in known in southern British Columbia, including the Similkameen Batholith, the Kruger syenite, and the Lost Horse syenite. Further study of these coeval plutons may constrain tectonic processses occurring at this time in the Canadian Cordillera. 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.831.1-0052531/manifest

Comment

Related Items