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Stable isotopes as an exploration tool : tracking cryptic alteration surrounding the Iscaycruz Zn (Pb-Cu-Ag) skarn-CRD deposit, central Peru

University of British Columbia

Proximal stable isotope haloes have been identified surrounding central Peruvian deposits including the Antamina Zn-Cu skarn and the Uchucchacua Ag-base metal veins. Studies analyzing stable isotopes around mineral deposits observed consistent alteration haloes of carbonate rocks with relatively depleted δ¹⁸O values proximal to the center of mineralization and areas of increased fluid:rock interaction. The Iscaycruz Zn-(Pb-Cu-Ag) skarn-carbonate replacement deposit is located within a sequence of Early Cretaceous, layered carbonate and siliciclastic rocks in central Peru. A primary goal of this study was to integrate visible and cryptic alteration around a known ore body and utilize the identified relationships as an exploration tool for regional targets. The stable isotopes of carbon and oxygen were used to identify asymmetric haloes of isotopic alteration surrounding fluid flow pathways, primarily lithologic contacts, east-west faults, and east-northeast faults. The extent of isotopic alteration perpendicular to bedding was 5-20 meters. In contrast, isotopic alteration was detectable along strike for 1-4 kilometers with local variation. Prior work at Iscaycruz utilized comparative mineralogy and fluid inclusions to infer that Iscaycruz deposits formed from a centralized mineralizing system below the Tinyag deposit. Stable isotopes of carbon, oxygen, and lead were used to provide additional lines of evidence that the deposits shared a single fluid source. A secondary goal is to evaluate sampling strategies to inform industry best practices. As a result, the isotopic alteration patterns were compared to visible alteration, UV luminescent response, and vein generation. Red fluorescent calcite was 100% correlated with extremely depleted δ¹⁸O values and show promise as a reliable cryptic alteration indicator for ore-related fluids. The sampling and analysis strategy employed in the thesis suggests that a simpler, more cost-effective strategy could be implemented to identify most of the patterns. For Cordilleran settings, a finite number of samples would be better utilized in many short transects across the contact instead of fewer, wider transects. These transects would collect samples perpendicular to the feature for only several meters in most cases, collecting more samples at a subset of transects to ensure that the limits of any pervasive alteration haloes may be detected as well.

Text

2020-01-17

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/73340

Geological Sciences

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/