Arc Minerals' geologist described the higher grade intersections from its widely spaced drilling at Cheyeza as located within a black saprolite thought to be the result of deep oxidation and supergene processes
have formed an apparent sub-surface, secondary oxide tabular shaped body, that appears to have been influenced meteoric waters.
However, REE fractionations and redistributions have been reported from various bauxite deposits due to evolution of geochemical systems in various mechanisms and conditions such as mobilization of REE, supergene processes
, surficial weathering, diagenetic processes, presence of REE-bearing mineral phases, pH of solutions and/or depositional environment, and existence of organic and/or non-organic complexing ligands (Mondillo et al., 2011; Abedini and Calagari, 2013; Mongelli et al., 2014, 2016, 2017; Liu et al., 2016; Buccione et al., 2016; Hou et al., 2017; Khosravi et al., 2017; Long et al., 2017; Radusinovic et al., 2017; Torro et al., 2017; Yuste et al., 2017; Chen et al., 2018).
The data portrayed in this manner indicates that the copper isotopic composition of chalcocite can be related to deposit types, with values less than -1% most likely related to sedimentary copper deposits, whereas values greater than +1 [per thousand] are most likely formed under supergene processes. To further detail variations in copper isotope compositions between the two genetically distinct, lower temperature deposits, a deposit specific comparison is presented in Figure 2, with 1[sigma] variations calculated by the standard deviations of all presented data.
Fantle, "Copper isotopic perspectives on supergene processes: Implications for the global Cu cycle," Elements, vol.
The ore minerals in these deposits are scattered throughout host rock as what is called disseminated mineralization or they are largely or wholly restricted to quartz veinlets forming a ramifying complex called stockwork; both forms of mineralization occur In many deposits Many alkaline and calc-alkaline porphyry Au-Cu deposits have extensive potassic hydrothermal alteration halos, varying both laterally and vertically, with changes in pressure, temperature, eH and pH during magmatic, hypogene and subsequent supergene processes
Arancibia, G., Matthews, S.J., and De Arce, C.P., 2006, K-At and [sup.40]Ar/[sup.39]Ar geochronology of supergene processes
in the Atacama Desert, Northern Chile: Tectonic and climatic relations: Journal of the Geological Society, London, v.
Galena and bournonite, in addition to sphalerite II and pyrite II, were the last minerals formed before supergene processes began.
In the small copper prospects that we have examined, the primary mineralogy is poorly known because strong supergene processes have masked it.
Macroscopic vermiculite formation was attributed to either hydrothermal (Morel, 1955) and/or supergene processes
(de la Calle and Suquet, 1988; Zhelyaskova-Panayotova et al., 1992, 1993; Fatma Toksoy-Koksal et al., 2001).
Although largely unaffected by supergene processes
, some Barstow specimens from the Mogul mine exhibit clusters of 0.5-mm, transparent pale yellowish hemimorphite crystals on sphalerite.
Among the recognized species, some 59 that contain copper are known to occur as a result of supergene processes
. The finest known examples of a number of supergene copper minerals were found at Bisbee: antlerite, bisbeeite, brochantite, chalcoalumite, claringbullite, conichalcite, crednerite, cuprite, delafossite, graemite, nantokite, paramelaconite, paratacamite, rosasite and spangolite.