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

Alkalic-type epithermal gold deposit model

“…In places, these large-scale faults may facilitate the formation of cross-orogen faults that are oblique to the stress direction (for example, Porgera, Golden Sunlight, Cripple Creek [Richards, 1995]). At the deposit scale, mineralization may be focused at the intersection of major faults (for example, Vatukoula; Begg, 1996), in vertical or steeply dipping structures (for example, Mayflower, Montana [Cocker, 1993]; Gies, Montana [Zhang and Spry, 1994]), or along shallowly dipping structures (for example, Tuvatu, Vatukoula). Brecciation zones are commonly the locus of high-grade mineralization (for example, Gies, Vatukoula).…”

“…For example, the Vatukoula deposit in Fiji is located at the intersection of the Tavua caldera boundary fault and a major shear zone (Anderson and Eaton, 1990). At the deposit scale, mineralization may occur at the intersection of major faults (for example, Vatukoula; Begg, 1996), in vertical or steeply dipping structures (for example, Mayflower, Montana [Cocker, 1993]; Gies, Montana [Zhang and Spry, 1994]), or shallowly dipping structures (for example, Tuvatu, Vatukoula). Zones of brecciation are commonly the locus of high-grade mineralization (for example, Gies, Vatukoula).…”

“…Wall-rock compositions (mafic or felsic, quartz-poor or quartz-rich, pelitic or carbonate) probably exert the most influence on the size of alteration halos. The Mayflower deposit in Montana consists of ore-bearing silicified dolomitic limestones up to 7 m wide that are surrounded by adularia, quartz, pyrite, and sericite (with or without roscoelite) alteration halos that are up to 10 m wide (Cocker, 1993). At the Cripple Creek deposit, nearly the entire diatreme (>30 km 2 ) has been altered to some extent, despite the much more spatially restricted distribution of high-grade mineralized zones ( fig.…”

Two new occurrences of benleonardite, a rare silver-tellurium sulphosalt, and a possible new occurrence of cervelleite

“…Grades of over 30 000 g/ton Au and Ag were encountered in isolated pockets. According to Cocker (1993) Benleonardite is a relatively common constituent of several samples of ore. In one specimen (M95-8) it is the most abundant mineral.…”

“…The Mayflower fault, in the vicinity of the telluride mineralization, abuts Late Cretaceous Elkhorn Mountain Volcanics, the Cambrian Wolsey (primarily limestone), and Flathead Formations (primarily cross-bedded sandstones and arkoses), and conglomerates of the Proterozoic LaHood Formation and is thought to be the major conduit for the hydrothermal fluids. Approximately 6,000 kg of Au have been extracted from the deposit to date but it remains open at depth (Cocker, 1993). Grades of over 30 000 g/ton Au and Ag were encountered in isolated pockets.…”