A genetic model for the H.Y.C. Deposit, Australia; based on regional sedimentology, geochemistry, and sulfide-sediment relationships

Abstract

The fine-grained, laminated, stratiform zinc-lead ores of the McArthur River (HYC) ore deposit have been the subject of continued debate in regard to the timing of zinc-lead mineralization. Early workers (e.g., Croxford and Jephcott, 1972;Lambert, 1976) considered the ores to be sedimentary-exhalative (sedex), while more recent researchers (e.g., Williams, 1978a;Eldridge et al., 1993; have argued for a syndiagenetic replacement origin. Several lines of evidence, including studies on the regional sedimentology, sediment geochemistry, nature of sulfide layering, paragenesis, and chemistry of base metal transport and deposition, are used here to demonstrate that a synsedimentary origin is likely for the HYC deposit.Studies on the regional sedimentology and geochemistry of the Barney Creek Formation have shown that the host rocks to the ore deposit, the HYC Pyritic Shale, represent a period of water deepening. Water depth was probably in excess of several hundred meters, with the deepest water euxinic facies corresponding to the ore position at the base of the HYC Pyritic Shale. A widespread manganese halo, developed in the W-Fold Shale Member below the ore horizon, is considered to relate to the start of the basin-deepening event, with manganese-bearing connate brines released into the basin along marginal rift faults. Manganese deposition occurred in the transitional dolomitic shale facies, where shallow-water, oxidized basin fluids intermittently mixed with deeper-water, reduced fluids along a redox interface. Sedimentary manganese deposition was immediately followed by zinc-lead mineralization in the deep-water, reduced facies of the HYC Pyritic Shale Member. The intimate relationship between the eight stratiform ore lenses and inter-ore sedimentary breccias indicates that sedimentary breccia deposition and ore formation are genetically linked. It is suggested that deep seismic events led to the following ore cycle: fault movement; sediment breccia deposition sourced from faults; episodic release of hot metalliferous brines along faults accompanied by sedimentary turbidites; and metal sulfide deposition in muds and turbidites adjacent to faults. The three modes of base metal sulfide occurrence in the ores, each considered by Eldridge et al. (1993) to have formed by replacement, are shown to have separate origins. The fine-grained sphalerite-galena bands (Mode 1) are intricately interlayered with pelagic organic-rich beds and thin turbidire beds. They exhibit classic sedimentary textures, such as load casts and flames, indicative of a synsedimentary origin. Coarser-grained Mode 2 base metal sulfides show complex intergrowths with nodular dolomite bands, and are considered to form by replacement during diagenesis. The discrete patches of coarse, Mode 3 base metal sulfides are interpreted to represent clastic input from turbidity currents sourced partly by the erosion of vein-style mineralization from the faulted margins of the basin.The detailed nature of the layering in the ores suggests that the introduction of m...

Effects of sulfide minerals on aromatic maturity parameters: Laboratory investigation using micro-scale sealed vessel pyrolysis

“…Mineralised sections of the deposit contain abundant fine-grained pyrite, sphalerite and galena (e.g. Large et al, 1998;Ireland et al, 2004).…”

Combined sulfur, carbon and redox budget constraints on genetic models for the Here’s Your Chance Pb–Zn deposit, Australia

“…This member is composed of dark, carbonaceous, pyritic, dolomitebearing laminated siltstones. Sedimentary structures within the HYC member include small scale cross lamination, scours, graded bedding, slumps [2][3][4] and syn-depositional faulting [20].…”

“…The relative importance of synsedimentary, syndiagenetic and epigenetic ore mineral deposition, and of the involvement of hydrothermal fluids, seawater and basin brines is controversial, in spite of extensive characterisation of mineral textures [2][3][4], isotopic compositions [5][6][7] and the organic geochemistry [e.g. [8][9][10][11].…”

“…4,12] (2); early diagenetic with ore precipitated within the sediments from sulfate-rich oxic metal-bearing hydrothermal fluids [9,10]. It is generally acknowledged that some combination of these processes may have operated [e.g.…”

Estimation and application of the thermodynamic properties of aqueous phenanthrene and isomers of methylphenanthrene at high temperature

“…The HYC ore deposit is a sediment-hosted base metal deposit that most likely formed as a consequence of infiltrating hydrothermal fluids from the Emu fault zone, to the north and north-east of the mine (Large et al, 1998), but the depths at which the fluids were sourced, and the degree to which the deposition of the metal sulfides in the ore deposit is syngenetic or epigenetic, continues to be a matter of debate (Logan et al, 2001). …”