Search

The Herberton Mineral Field hosts multiple small-scale, polymetallic Sn-Cu and Sn-Zn deposits. The Baal Gammon and Isabel polymetallic deposits in the Herberton Mineral Field contain early Sn that is overprinted by sulfides. At Baal Gammon, the sulfide overprinting is Cu-In-rich, whereas Isabel is a Zn-Pb-In-rich system. These deposits are hosted in the meta-sedimentary rocks of the Hodgkinson Formation and the porphyry dikes and volcanic rocks of the Kennedy Igneous Association. Primary Sn in these deposits occurs as cassiterite, which was altered to stannite during sulfide mineralization. The sulfide ores from Baal Gammon consist of chalcopyrite, pyrrhotite, and minor sphalerite, and sphalerite, galena, and minor chalcopyrite are observed at Isabel. Chalcopyrite from Baal Gammon contains on average 609 ppm Ag, 1194 ppm In, and 1410 ppm Sn, whereas chalcopyrite from the Isabel deposit contains on average 2302 ppm Ag, 725 ppm In, and 1042 ppm Sn. Sulfur isotope (δ34S) measurements of in-situ chalcopyrite-pyrrhotite mineral pairs show limited variation and low values that are indicative of a magmatic sulfur source with limited interaction with sulfur from connate and meteoric fluids during mineralization. The chalcopyrite and pyrrhotite δ34S values at the Baal Gammon deposit vary between 0.99–1.91‰ and 1.35–2.48‰, respectively. The δ34S values at the Isabel deposit vary between 0.91–1.45‰ for chalcopyrite and 1.12–2.11‰ for pyrrhotite. The trace element composition of major sulfides and sulfur isotopes of chalcopyrite and pyrrhotite combined with thermodynamic modeling indicates that the mineralizing fluids at the Baal Gammon and Isabel deposits have an igneous source, where the metals were transported as metal-chloride complexes at low pH (< 5) and below ~ 300 °C. The source of these sulfide-rich mineralizing fluids is most likely derived from the magmatic activity associated with the emplacement of the Slaughter Yard Creek Volcanics during a period of crustal thinning between 300 and 280 Ma. [ABSTRACT FROM AUTHOR]

The Herberton Mineral Field in Northeast Australia hosts world class magmatic-hydrothermal Sn–W polymetallic deposits that are enriched in In. The Baal Gammon and Isabel deposits from the Herberton Mineral Field contains early tin, as cassiterite, overprinted by sulfide mineralization as chalcopyrite, sphalerite, galena, pyrrhotite, and stannite. We investigated the distribution of In in the sulfide ores from these two deposits, calculated the temperature of formation via sphalerite-stannite geothermometer, and deduced the physicochemical conditions favorable for enriching In in this mineralizing environment. The Baal Gammon deposit is dominated by chalcopyrite, with In contained in chalcopyrite, sphalerite, and stannite. The average In concentrations measured by EPMA in chalcopyrite, sphalerite, and stannite are 0.10, 0.68, and 0.92 wt%, respectively. Chalcopyrite, pyrrhotite, and sphalerite textures indicate that In incorporation occurred during exsolution from an intermediate solid solution of cubanite composition. The Isabel deposit is dominated by sphalerite associated with galena and contains only minor amounts of chalcopyrite. The average concentration of In in sphalerite from the Isabel deposit is 0.11 wt%. The stannite-sphalerite geothermometer indicates mineralization temperatures of ~ 290 °C at the Baal Gammon deposit, and ~ 307 °C at the Isabel deposit. At these temperatures, the physicochemical modeling suggests that stable In chlorine complexes occur in acidic conditions (pH < 3). These results when combined with the Eh–pH phase model of the sulfide assemblage further constrain the redox conditions during mineralization. [ABSTRACT FROM AUTHOR]

Northeast Queensland contains multiple slices of mafic–ultramafic units, strung out along regional faults that mark major tectonic boundaries. One such complex is the Cowley Ophiolite Complex, which is situated along the Russell-Mulgrave Fault. The Cowley Ophiolite Complex is a differentiated mafic–ultramafic complex composed of gabbro, chlorite schist, anthophyllite schist and serpentinite. We interpret that the alteration assemblages observed throughout the Cowley Ophiolite Complex reflect an amphibolite facies metasomatic overprint within a supra-subduction zone setting. This interpretation is consistent with geochemical discrimination of the gabbro, and chromite grains from the anthophyllite schist. The Cowley Ophiolite Complex records a higher metamorphic grade than the surrounding Hodgkinson Formation, and we interpret this to reflect the allochthonous structural setting of the complex, positioned along an ancient subduction margin. This subduction margin is represented today by the Russell-Mulgrave Fault. Metasomatism and emplacement of the complex probably pre-dated deposition of the Mossman Orogen's active margin successions. Our interpretation of an active subduction complex, which pre-dated the formation of the Mossman Orogen, suggests that the Russell-Mulgrave Fault is a Paleozoic, continental suture zone. The Cowley Ophiolite Complex presents little indication of economic mineralisation; however, much of the complex remains unexplored. The Cowley Ophiolite Complex is a differentiated, mafic–ultramafic complex formed within a supra-subduction zone setting. Emplacement of the Cowley Ophiolite Complex, along the Russell-Mulgrave Fault, pre-dated the formation of the Hodgkinson Province. The Russell-Mulgrave Fault represents an ancient subduction margin, and is interpreted as a Paleozoic, continental suture zone. [ABSTRACT FROM AUTHOR]

[Display omitted] • The geological setting of indium-rich deposits (Baal Gammon and Isabel) of the Herberton Mineral Field, northeast Queensland, Australia is presented. • New geochronological data from the granite supersuites that occur in the Herberton Mineral Field are reported. • Tectonic synthesis of the Herberton Mineral Field shows that tin mineralization occurred during compression, while sulfides and indium mineralization occurred during crustal extension. Base metal mineralization at the Baal Gammon and Isabel deposits of the Herberton Mineral Field (HMF) is hosted in metamorphosed greywacke beds in the Hodgkinson Formation, which were intruded by granite, porphyry dykes and overlain by volcanic rocks of the Kennedy Igneous Association during the Carboniferous and Permian. The tin mineralization at the Baal Gammon deposit is hosted by a silicified, chlorite-altered, quartz-feldspar porphyry (UNA Porphyry). The tin mineralization at the Isabel deposit is in polymetallic veins hosting disseminated cassiterite. Polymetallic sulfides (Cu-Zn) and indium (In) mineralization at both deposits overprint the tin mineralization. Chalcopyrite, sphalerite, and stannite host indium in the polymetallic sulfide assemblage at both deposits. Based on overprinting relationships, the timing of tin mineralization is related to the magmatic activity at ca. 320 Ma, whereas the sulfide and indium mineralization are most likely associated with the emplacement of porphyry dykes at ca. 290 Ma. The overall magmatic activity in the HMF spreads between ca. 365 and 280 Ma, with peaks at ca. 337, 322, 305, and 285 Ma. The change from tin mineralization at ca. 320 Ma to sulfide and indium mineralization at ca. 290 Ma indicates a transition from a compressive to an extensional tectonic regime. [ABSTRACT FROM AUTHOR]

High-tech metals including Ge, Ga and In are often sourced as by-products from a range of ore minerals, including sphalerite from Zn-Pb deposits. The Hilton Zn-Pb (Ag) deposit in the Mount Isa Inlier, Queensland, contains six textural varieties of sphalerite that have formed through a diverse range of processes with variable co-crystallising sulphides. This textural complexity provides a unique opportunity to examine the effects of co-crystallising sulphides and chemical remobilisation on the trace element geochemistry of sphalerite. Early sphalerite (sph-1) is stratabound and coeval with pyrrhotite, pyrite and galena. Disseminated sphalerite (sph-2) occurs as isolated fine-grained laths rarely associated with co-crystallising sulphides and represents an alteration selvage accompanying the precipitation of early stratabound sphalerite (sph-1). Sphalerite (sph-3) occurs in early ferroan-dolomite veins and formed from the chemical remobilisation of stratabound sphalerite (sph-1) during brittle fracturing and interstitial fluid flow. This generation of veins terminate at the interface, and occurs within clasts of the paragenetically later sphalerite-dominated breccias (sph-4). Regions of high-grade Cu (>2%) mineralisation contain a late generation of sphalerite (sph-5), which formed from the recrystallisation of breccia-type sphalerite (sph-4) during the infiltration of a paragenetically late Cu- and Pb-rich fluid. Late ferroan-dolomite veins crosscut all previous stages of mineralisation and also contain chemically remobilised sphalerite (sph-6). Major and trace elements including Fe, Co, In, Sn, Sb, Ag and Tl are depleted in sphalerite associated with abundant co-crystallised neighbouring sulphides (e.g., pyrite, pyrrhotite, galena and chalcopyrite) relative to sphalerite associated with minor to no co-crystallising sulphides. This depletion is attributed to the incorporation of the trace elements into the competing sulphide minerals. Chemically remobilised sphalerite is enriched in Zn, Cd, Ge, Ga and Sn, and depleted in Fe, Tl, Co, Bi and occasionally Ag, Sb and Mn relative to the primary minerals. This is attributed to the higher mobility of Zn, Ge, Ga and Sn relative to Fe and Co during the chemical remobilisation process, coupled with the effect of co-crystallising with galena and ferroan-dolomite. Results from this study indicate that the consideration of co-crystallising sulphides and post-depositional processes are important in understanding the trace element composition of sphalerite on both a microscopic and deposit-scale, and has implications for a range of Zn-Pb deposits worldwide. [ABSTRACT FROM AUTHOR]