Invisible Gold Paragenesis and Geochemistry in Pyrite from Orogenic and Sediment-Hosted Gold Deposits

Abstract

LA-ICPMS analysis of pyrite in ten gold deposits is used to determine the precise siting of invisible gold within pyrite, and thus the timing of gold introduction relative to the growth of pyrite and related orogenic events. A spectrum of invisible gold relationships in pyrite has been observed which suggests that, relative to orogenic pyrite growth, gold introduction in some deposits is early at the start of pyrite growth; in other deposits, it is late toward the end of pyrite growth and in a third case, it may be introduced at the intermediate stage of orogenic pyrite growth. In addition, we report a distinct chemical association of invisible gold in pyrite in the deposits studied. For example, in the Gold Quarry (Carlin type), Mt Olympus, Macraes and Konkera, the invisible gold is principally related to the arsenic content of pyrite. In contrast, in Kumtor and Geita Hill, the invisible gold is principally related to the tellurium content of pyrite. Other deposits (Golden Mile, Bendigo, Spanish Mountain, Witwatersrand Carbon Leader Reef (CLR)) exhibit both the Au-As and Au-Te association in pyrite. Some deposits of the Au-As association have late orogenic Au-As-rich rims on pyrite, which substantially increase the value of the ore. In contrast, deposits of the Au-Te association are not known to have Au-rich rims on pyrite but contain nano-to micro-inclusions of Au-Ag-(Pb-Bi) tellurides.solution As, known as arsenian pyrite [9,10]. Arsenic can substitute into either the Fe site or the S site in pyrite and a maximum of 8%-11% As has been reported [11][12][13]. The position of ionic gold in the structure of pyrite is still not clear, although it is assumed that ionic gold Au + substitutes for iron, entering distorted octahedral sites, whereas As substitutes for S in the tetrahedral sites [8]. Both surface speciation, and distortion-expansion of the pyrite lattice by incorporation of As are considered to be key processes in Au accumulation by arsenian pyrite [8,14].A landmark publication [4] defined a relationship between the amount of invisible solid solution gold in pyrite and its arsenic content, using a database of analyses of pyrite from several Carlin and epithermal deposits. This maximum limit of invisible gold, from pyrite formed in the temperature range of 150 to 250 • C, is approximately 100 ppm Au for 2000 ppm As, and 1000 ppm Au for 2% As, and has become known as the saturation line for Au in arsenian pyrite (Figure 1; [4]). Gold analyses of pyrite that plot above the saturation line indicate free gold as nano-to micro-inclusions in pyrite. More recent research [5] has shown that the gold saturation line is most probably controlled by a number of factors, possibly including the crystal chemistry of pyrite and fluid/rock interactions and therefore different positions of the gold saturation line may need to be defined for each gold deposit type.Minerals 2020, 10, x FOR PEER REVIEW 2 of 21 solution As, known as arsenian pyrite [9,10]. Arsenic can substitute into either the Fe site or the S site in pyrite a...

Genesis of Carbonate Breccia Containing Invisible Gold in Taebaeksan Basin, South Korea

“…The gold content of the pyrite (0.01-1.54 wt%) and hematite (0.07 wt%) ranges from 0.01 to 1.54 wt% (Table 3). These properties are similar to the general characteristics of invisible gold from Carlin-type gold deposits ( [31,32] and references therein). The second type of gold is distributed within pyrite and hematite (after pyrite).…”

“…In the Yemi breccia, invisible gold was discovered (Figure 7). This phenomenon is reported in hydrothermal Carlin-type gold deposits [31][32][33][34]53,54]. In particular, gold within pyrite and hematite (after pyrite) and isolated gold particles ( Figure 7) have been reported in the Shuiyindong deposit [33,34], which is a Carlin-type hydrothermal gold deposit.…”

Types of Tellurium Mineralization of Gold Deposits of the Aldan Shield (Southern Yakutia, Russia)

“…Numerous studies show the presence of gold of three varieties: invisible in pyrite or arsenopyrite, native gold and gold tellurides. With the advent in recent decades of the highly sensitive inductively coupled plasma mass spectrometry (LA-ICP-MS) method and, especially, the local version of this method with laser ablation of the substance directly from the sample, it became possible to determine gold and other trace elements in pyrite [45][46][47][48][49].…”

Editorial for Special Issue “Pyrite Varieties and LA-ICP-MS Geochemistry in Ore Genesis and Exploration”

“…In our review paper [1], we attempted to determine the timing and chemical association of Au relative to the growth of pyrite aggregates from successive orogenic fluid events through a combination of textural studies of pyrite, with LA-ICPMS mapping and spot analyses of eleven orogenic deposits. A spectrum of invisible gold relationships in pyrite has been observed, which suggests that relative to orogenic pyrite growth, gold introduction in some deposits is early at the start of pyrite growth; in other deposits, it is late toward the end of pyrite growth, and in a third case, it may be introduced at the intermediate stage of orogenic pyrite growth.…”

“…The idea that pyrite varieties are a very useful record of geochemical, geological and ore-forming processes is certainly not new. However, the capabilities of the present-day LA-ICP-MS method in terms of high sensitivity and using mapping of trace elements continues to provide new insights into how these ore-forming processes take place, and in what order, during formation of gold [1], massive sulfide [2,3] and other deposits. This method yields plentiful trace element data on pyrite varieties in oil shales, which could be useful to develop inorganic-organic models of oil formation and predict the metal potential of adjacent pyrite mineralization [4].…”