Primary element dispersion patterns in a carbonate-hosted, epithermal, high-grade, Au-Ag telluride system: Mayflower Mine, Madison County, Montana, USA

Abstract

Primary element dispersion patterns at the Mayflower Mine, Montana, are related to Au-Ag telluride mineralization in vertical to overturned, hydrothermally altered carbonates of the Middle Cambrian Meagher Formation, and are in accord with mineralizing fluids principally having been guided by stratigraphic and structural conduits. Proximity of the Mayflower mineralization to the Mayflower fault, which overlies and parallels the Proterozoic Willow Creek fault system, and lateral geochemical zoning along strike of the Meagher Formation away from the fault suggest that the Mayflower fault was a primary conduit for hydrothermal fluids. Carbonates of the Meagher Formation are enriched in Cu, Pb, Ag, Au and V near the Mayflower fault and in Mn and MgO at greater distances. Hg, Tl, As, and Zn tend to be constant or slightly greater with increasing distance. Primary element dispersion patterns and hydrothermal alteration are centered on and zoned relative to detrital quartz-bearing, paleotidal channels in the Meagher Formation. Zoning consists of: (1) a central zone of quartz, adularia and roscoelite containing elevated concentrations of Hg, Tl, As, Cu, Te, V, Zn, Mo, and Pb; (2) a proximal zone of quartz and adularia with anomalous Hg, Tl, As, and Cu; and (3) a distal zone of hydrothermal dolomite with anomalous Mn. The quartz-adularia and dolomite zones are significantly higher in SiO 2 and K 2O, and MgO respectively relative to unaltered carbonates. Gold and silver were best developed in and adjacent to the central zone. Progressively larger base-metal and silver values from the surface to the presently explored depth of 670 m suggest mineralizing fluids also traveled vertically within the paleotidal channels. The primary element dispersion patterns appear to be controlled by: (1) lithology (permeable, paleotidal channels), (2) structure (deep-seated, Mayflower fault which acted as a fluid conduit), and (3) distance from source.