The Origin of Chlorite-Tremolite-Carbonate Rocks Associated with the Thalanga Volcanic-Hosted Massive Sulfide Deposit, North Queensland, Australia

Abstract

Thalanga is located near the western end of the Mount Windsor subprovince-a belt of deformed marine sedimentary and AbstractThe Thalanga polymetallic massive sulfide deposit is hosted by felsic volcanics of the Cambro-Ordovician Mount Windsor subprovince in North Queensland. The sheetlike sulfide deposit consists of several semiconnected lenses, totaling 6.6 million metric tons (Mt), which lie at a single stratigraphic level between underlying subaqueously emplaced rhyolite and overlying dacitic to andesitic lavas, sills, and volcaniclastic rocks. The ores and host rocks have been deformed and metamorphosed to upper greenschist facies. Associated with the West Thalanga orebody are strata-bound lenses composed of chlorite, tremolite, dolomite, and calcite that previously have been interpreted as exhalites. They extend up to a few hundred meters along the mineralized horizon and locally also exist in the stratigraphic footwall around the fringes of the deposit.Rhyolitic volcanics beneath the deposit are extensively altered. A pervasive sericite ± chlorite ± pyrite zone that extends greater than 200 m into the footwall envelops semistratiform proximal quartz + pyrite ± chlorite stringer zones. Major and trace element geochemical data indicate that Zr, Ti, and Al remained essentially immobile in the footwall rocks despite intense hydrothermal alteration involving significant mass transfers of mobile elements.The chlorite + tremolite + carbonate assemblages associated with ore lenses have immobile element ratios identical to those of the altered rhyolites. Carbonate-rich assemblages retain some relict spheroidal and rhombic textures in dolomite, which suggest formation at an early hydrothermal stage in a matrix of chlorite or in open spaces.The chlorite + tremolite + carbonate rocks probably represent metamorphic equivalents of hydrothermal chlorite + quartz + dolomite + calcite (or Mg smectite + quartz + dolomite + calcite) assemblages. The formation of tremolite by metamorphic reaction of quartz and dolomite is consistent with regional metamorphic conditions. With allowance for metamorphic decarbonation, carbon and oxygen isotope data from dolomite and calcite are consistent with precipitation of primary dolomite at 170°to 250°C from seawater-dominated fluid.The chlorite + tremolite + carbonate rocks at Thalanga are consequently reinterpreted as altered rhyolitic volcaniclastics, containing variable proportions of hydrothermal carbonate. They probably formed in a zone of mixing of hydrothermal fluid and seawater, in a permeable substrate close to the paleosea floor. Siliceous ironstones that are present in distal parts of some Thalanga ore lenses have very low immobile element contents and are probably true exhalites. West Extended West Thalanga Central Thalanga Vomacka East Thalanga Far East 500 m V = H FIG. 2. Vertical longitudinal projection showing distribution of Thalanga sulfide lenses.

Facies architecture of the felsic lava‐dominated host sequence to the Thalanga massive sulfide deposit, Lower Ordovician, northern Queensland

“…Carbonate–tremolite–chlorite rocks that represent metamorphosed intense alteration of footwall rhyolite (Herrmann 1994) are common in West Thalanga (section 2) but scarce elsewhere. In West Thalanga, carbonate, tremolite and chlorite are also the dominant gangue minerals in massive sulfides.…”

Lewis Ponds, a hybrid carbonate and volcanic-hosted polymetallic massive sulphide deposit, New South Wales, Australia

“…Lewis Ponds has similar features to other eastern Australian, stratabound VHMS deposits, including Rosebery, Woodlawn, Thalanga and Mount Chalmers (McKay and Hazeldene 1987;Large 1992;Herrmann and Hill 2001;Large et al 2001a). A number of small massive sulphide deposits in the Lewis Ponds district (Fig.…”

“…Spheroids, rhombs and anhedral dolomite 3 crystals grow during low temperature (60-150°C) dolomitization of carbonate-rich sediment (Radke and Mathis 1980;Gregg and Sibley 1984). Diagenetic or hydrothermal carbonate assemblages form at the periphery of stratabound VHMS deposits due to mixing between hydrothermal fluids and cooler seawater (Herrmann and Hill 2001;Large et al 2001a) and throughout Mississippi Valley Type and Irish-style deposits due to reactions with the host limestone (Misra et al 1997;Hitzman et al 2002;Peace et al 2003). Carbonate solubility decreases with increasing temperature in low salinity fluids (Rimstidt 1997).…”

“…Mineralogical trends in the Toms Zone footwall are similar to many eastern Australian stratabound VHMS deposits. Sericite-rich assemblages surround a chloriterich core at Rosebery (Large et al 2001a), Thalanga (Herrmann and Hill 2001), Currawong (Bodon and Valenta 1995) and Captains Flat (Davis 1990). Systematic variations in chlorite Mg number have been documented at VHMS deposits in Australia, Japan and Canada (Urabe et al 1983;McLeod and Stanton 1984;Paulick et al 2001).…”

Intermittent pneumatic compression pump in upper extremity impairments of breast cancer-related lymphedema

“…Textural (e.g., Khin & Large 1992;Sharpe & Gemmell 2001) and chemical evidence (e.g., Herrmann & Hill 2001;Large et al 2001) imply that direct precipitation is not as important as void infilligs and selective replacements of the volcanic components on the sea floor. In these cases, formation of carbonate minerals involves mixing of hydrothermal fluids and seawater below the sea floor in permeable volcanic units (e.g., Hermann & Hill 2001).…”