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The metamorphism of the rocks of the Aldridge formation, Kimberley B.C Hoadley, John William

Abstract

The area near the Sullivan Mine, Kimberley B.C., is underlain by rocks of the Purcell series which consist of two sedimentary formations of late Pre-Cambrian age, the Aldridge and the Creston. Both are composed of argillite, siltstone, and quartzite. The Sullivan ore body is a replacement deposit in certain favourable horizons in the Aldridge formation. The only known igneous rocks near the mine are the Purcell intrusives of late Pre-Cambrian age. These intrusives occur as large sheets, or sills, at a small angle to the bedding of the Purcell series.They are chemically about the same as gabbro. The object of this research was to determine the changes induced in the sedimentary rocks of the Aldridge formation near the Sullivan Mine by the intrusion of the Purcell sills; to compare the alterations found with the alterations known to be present in the wall rocks of the Sullivan ore body; and from this comparison, determine whether there is any justification for relating the mineralization of the Sullivan ore body to the intrusion of the Purcell sills. In order to obtain the information required the writer made a petrographic examination of thirty-six thin sections of specimens of the core of the Sullivan Diamond Drill Hole 249 located just east of the mine. The hole was drilled vertically through a sixty foot sill, and on into the underlying sediments of the Aldridge formation. The results obtained from this examination indicate that the sediments adjacent to the sill have been subjected to low grade thermal metamorphism, which has resulted in the development of a pronounced biotite spotted contact zone. Late magmatic emanations, either from the partially consolidated sill, or from the parent magma chamber caused metasomatism in the sedimentary rocks of the contact zone, and the effects of the metasomatic action are super imposed upon the effects of the thermal metamorphism. Tourmaline, albite, pyrrhotite, sphalerite, sphene and rutile are the main minerals produced by the hydrothermal action. A comparison of the alterations found in these sedimentary rocks examined, with the alteration present in the Sullivan ore body and its wall rocks, reveals a distinct similarity. This similarity, plus the fact that the drill hole is within one half mile of the mine suggests a common origin for the magmatic solutions. Therefore, the solutions which produced the Sullivan Mine ore body may have been genetically related to the Purcell intrusives.

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