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Abstract:

The advent of LA ICP-MS analysis has provided a means to investigate both the distribution and relative timing of trace elements during the growth of sulfides in hydrothermal ore systems. This technological advance precludes the inherent problems associated with whole-rock analyses which dilute elemental abundances and mask their associations, both of which are critical to interpreting geochemical data in the context of the evolution, fingerprinting and discrimination ore systems. Here we introduce the concept of integrating the results of standard elemental mapping of common sulfides phases in gold systems, which provide a sense of relative paragenesis (e.g., Co-Ni-As and Au-Ag-Te associations), with time domain slices (TDS; time for each complete analysis in traverse mode) of the same laser traverse mode data to provide a proxy for individual point analysis. The TDS data are then used to generate a series of bivariate plots to assess elemental associations not readily visible in the element maps. Such an example is Au versus Ag which reveals such important information as: 1) variation of Au:Ag ratios within and between deposit types, and 2) presence of both invisible and particulate gold with the same Au:Ag ratio. By combining the latter plots with multi-dimensional element distribution plots and various statistically generated diagrams, details of elemental associations are also revealed. The latter indicate that the elemental paragenesis in gold systems is far more complex than generally considered, are protracted, and involve the infiltration of external fluids. This information provides insight into such processes as zone refining, element remobilization, and infiltration of externally derived fluids as indicated by the association of Ag-rich alloys (Bi, Sb, Te) with elevated Al, Mn, Ti (also seen on the element maps). Thus the results of analyzing sulfides from a variety of gold deposit settings (e.g., orogenic vs. intrusion-related) indicate that classification of gold deposit types using such data, while challenging, does provide insight into important processes and may provide insight into discriminating gold deposit settings once a database is established.

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GeoRef, Copyright 2018, American Geological Institute.<br/>2017-013917