Lithological and Structural Controls on the Form and Setting of VeinStockwork Orebodies at the Mount Charlotte Gold Deposit, Kalgoorlie

Abstract

The Mount Charlotte quartz vein gold deposit comprises a series of steeply plunging, pipelike vein stockwork orebodies in massive metagabbro. The orebodies are strata bound to the most differentiated unit of the host sill and are typically adjacent to major steeply dipping faults that cut the sill. The stockworks have two sets of veins with a dihedral angle of about 50°that developed as hydraulic fractures, filled simultaneously, and are generally approximately equally developed. Veins crosscut major faults and parallel minor faults of two sets but are cut along reactivated fault surfaces. The fault sets were inactive during mineralization and are neither veined nor are loci of zones of intense alteration. Rare faults of a third set are in part veined and are loci of zones of mineralization. Two interpretations of the stress regime during vein formation are based on different models of fracture formation. For both stress regimes, the major fault sets are relatively unfavorably oriented for slip or dilation, and predicted movement vectors do not fit fault-plane lineations. The lack of fault activity during ore fluid flow promoted formation of vein stockworks at Mount Charlotte rather than shear zone or fault-hosted veins. Fluid flow paths and orebody siting are controlled by stress-guide effects due to the rheology of the host gabbro, and by the three-dimensional geometry of impermeable faults and of fault-bounded blocks of rock.

Rock-Buffering of Auriferous Fluids in Altered Rocks Associated with the Golden Mile-Style Mineralization, Kalgoorlie Gold Field, Western Australia

“…The hematite-free assemblage, which is the same as that observed in carbonate alteration related to the Golden Mile mineralization, was predicted to be stable over a wide range of the conditions investigated. Pyrrhotite, which is predicted by the modeling at temperatures greater than 380°C, is not observed in the alteration associated with the Golden Mile mineralization but it is documented in Mount Charlotte-style alteration a few kilometers to the north (Ridley and Mengler, 2000;Bateman and Hagemann, 2004). Golden Mile alteration commonly contains hematite and magnetite in textural equilibrium (Clout et al, 1990;Phillips and Gibb, 1993), but this is not predicted by the model.…”

“…The large size of the gold field has led to numerous studies of the deposits, and a large amount of deposit-related data has been collected over the last 100 years (e.g., Travis et al, 1971;Phillips et al, 1996;Bateman et al, 2001;White et al, 2003;Bateman and Hagemann, 2004). Three main styles of gold mineralization have been distinguished in the Kalgoorlie gold field (Boulter et al, 1987): Golden Mile (similar to Fimiston-style of Bateman and Hagemann, 2004), Oroya, and Charlotte (Ridley and Mengler, 2000). Over 70 percent of gold production has come from Golden Mile mineralization (Boulter et al, 1987;Bateman et al, 2001), and that mineralization is the subject of this study.…”

Prediction of hidden ore bodies by synthesis of geological, geophysical and geochemical information based on dynamic model in Fenghuangshan ore field, Tongling district, China

“…The controls of mechanical dilation on the focussing of the ore fluids, and the location of hydrothermal ore bodies, have been well documented (Rice, 1975;Rudnicki, 1984;Ord and Oliver, 1997;Ridley and Mengler, 2000;Upton, 1998). In the Fenghuangshan ore field, the ore bodies are also located in the dilation zones, as indicated by brecciation of wall rocks at both the mine scale (Figs.…”

Fluids and Ore Formation in the Earth's Crust

“…At the scale of alteration zones around veins, chemical diffusion through the pore fluid may be even faster than heat diffusion. The width of such haloes has been used by Cathles and Shannon (2007) to argue that formation of veins, and possibly major magmatic-hydrothermal orebodies, may require as little as 10-100 years (see also Ridley and Mengler, 2000, for veins shown in Figure 2D). …”

“…The first involves removal of H2S and consequent de-complexation of gold. This can occur by reaction with Fe-rich wall rocks to form pyrite (a major mechanism in metamorphogenic gold quartz lodes; Phillips and Groves, 1983;Ridley and Mengler, 2000) or by low-pressure boiling whereby H2S escapes into the gas phase, forming epithermal gold veins (Drummond and Ohmoto, 1985;Spycher and Reed, 1989). Second, the reduction of a mildly oxidized gold-rich (e.g., magmatic) fluid by reaction with organic carbon (or mixing with methane) can explain gold precipitation, commonly in association with other redox-sensitive elements such as Sb or As.…”