Assessing the Potential for Carlin-type Gold in Northern Nye County, Nevada
AuthorSelwood, Robert Daniel
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Through the synthesis of regional stream sediment geochemistry and regional geologic maps using fuzzy logic-based mineral potential mapping, this study assesses the potential for Carlin-type mineral systems in northern Nye County. Robust factor analysis (FA) is applied to log ratio-transformed stream sediment geochemical data to identify regional mineralogical processes in northern Nye County, including geochemical patterns indicative of hydrothermal mineralization. The data analysed comprise new multielement analyses of 2,222 stream sediment samples over the study area. Several geochemical processes can be inferred from latent factors extracted from these data including degree of magmatic fractionation, Au-As-Sb-Tl mineralization, marine sedimentation depth, reduction by organic matter, heavy mineral concentration, and W mineralization. Spatial analysis of factor scores using thematic drainage maps show a close spatial correlation between their inferred geochemical process and rocks that formed by those processes. Significantly, strongly negative scores for factor 2, characterized by negative loadings (> -0.25) of Sb-As-W-Tl-Mo-U-Au, are spatially associated with known occurrences of Carlin-type, carbonate-hosted, and ow sulfidation epithermal gold mineralization.A total of 119 drainage basins are highlighted as geochemically prospective for Carlin-type mineralization through FA. However, this technique does not differentiate between Carlin-type, carbonate-hosted, and low sulfidation epithermal gold systems. To improve the efficacy of factor 2 as a means of evaluating the exploration potential for Carlin-type mineralization, scores are combined with prospective stratigraphic horizons for Carlin-type mineralization in a fuzzy logic based mineral potential model.Ten areas are highlighted in this model as having potential for carbonate-hosted gold mineralization, and are described in terms of tectonic and igneous setting, structural setting, host rocks, controlling structures, hydrothermal alteration, mineralization styles, ore mineralogy, and geochemistry. When compared with Carlin-type mineral systems at the regional scale, these carbonate-hosted gold deposits share many similarities: 1) they occur along the same rifted cratonic margin, 2) all are partly hosted within stratigraphic packages that contain permeable and reactive carbonate rocks, 3) all have a spatial association with Cenozoic magmatism, and 4) all share a similar regional geochemical signature characterized by As, Sb, Tl, and Au. However, when compared at the deposit scale, carbonate-hosted gold deposits in northern Nye County differ from Carlin-type gold systems in the following ways: 1) they lack low-angle geometries associated with the replacement of reactive carbonates along tectono-stratigraphic and stratigraphic horizons; 2) while hosted in equivalent Paleozoic strata, they are also partly hosted in Paleogene volcanic rocks; 3) carbonate dissolution is spatially limited to narrow margins along high angle structures and jasperoid formation is far more extensive; 4) jasperoid quartz commonly exhibits quartz textures indicative of an amorphous silica precursor phase that may indicate localized boiling in some systems, and 5) pyrite observed in jasperoid bodies, while arsenic-rich, lacks the growth bands characteristic of Carlin-type gold deposits.These differences have profound implications for the prospectivity of carbonate-hosted gold deposits in the study area, suggesting limited water-rock reactions within these mineral systems and therefore limited potential to form Carlin-type gold deposits that are characteristically low-moderate grade high tonnage deposits. However, quartz textures that provide evidence for boiling in these mineral systems are more consistent with epithermal systems and may indicate potential for high grade, structurally controlled gold deposits.