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Author: Admin | 2025-04-27
Of the economic geology community. Here we summarize a few minerals that are being used, or have the potential to be used, in sediment HMC surveys. Zircon occurs in the heavy non-magnetic HMC sediment fraction. Some trace element compositions of zircon (Ce4+/Ce3+ ratio) are recognized to be related to the oxidation state of magmas, suggesting magma fertility potential. High values indicate a more oxidized state (Ballard et al. 2002). Shen et al. (2015) found that larger porphyry Cu deposits (>1.5 Mt Cu metal) are associated with more oxidized intrusions with higher Ce4+/Ce3+ ratios (>120). Shu et al. (2019) reported a similar relationship between this ratio (and other zircon trace element parameters) and the metal tonnage of porphyry and skarn Mo deposits. Loucks et al. (2020) proposed another redox state indicator using the concentrations of Ce, Ti and age-corrected initial U in zircons. Detrital zircon in stream sediments was applied by O'Reilly et al. (2004) to infer the age, crustal evolution and fertility of the corresponding catchment lithologies via their method, TerraneChron, which integrates zircon U–Pb age dates, Hf isotopic composition and trace element composition. Garnet occurs in the paramagnetic heavy fraction of HMC and its chemistry may indicate both lithological information and mineral prospectivity. Andraditic garnet is derived from skarns, whereas grossularitic garnet, with or without spessartine components, may be from either skarn or marble (Meinert et al. 2005; Chang et al. 2019). Metamorphic garnet is likely rich in almandine endmember pyrope garnet. Cr-pyrope (including G9/G10 compositions) is an accepted indicator mineral for diamond-bearing kimberlites (Nixon 1980; Grutter and Menzies 2003; Grutter et al. 2004). Two examples of successful diamond exploration using stream sediment HMC are summarized in Case history 5. Apatite is semi-resistate and also of marginal density (3.15–3.20 g cm−3), occurring in the intermediate-density and non-magnetic HMC fraction. Because it is difficult to separate from other rock-forming minerals in the indicator mineral processing, identification of apatite grains is particularly enhanced by use of automated SEM techniques. Apatite is a common mineral in igneous, metamorphic and sedimentary rocks, and in various types of deposits including magmatic magnetite–apatite deposits, carbonatite deposits, sedimentary apatite deposits and hydrothermal deposits including iron–oxide–copper–gold (IOCG), iron–oxide–apatite Kiruna deposits, porphyry, skarn, epithermal, diamond and orogenic gold deposits. There have been extensive studies of apatite chemistry (summarized in Belousova et al. 2002). The research relevant to mineral exploration includes: (1) distinguishing different types of hydrothermal deposits (Mao et al. 2016); (2) discriminating magmatic apatite and hydrothermal apatite from different alteration zones in some porphyry deposits using apatite trace element composition and cathodoluminescence colours (Bouzari et al. 2016); (3) inferring the F, Br and I concentrations of the fluids if an apatite is known to be hydrothermal (Kusebauch et al. 2015); and (4) inferring magma fertility using apatite S and Cl contents (Peng et al. 1997; Chelle-Michou and Chiaradia 2017; Meng et al. 2021). Magma fertility may also be inferred by magma redox state and its evolution based on Mn in apatite (Miles et al. 2014) or S
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