Paragenetic Association of Platinum and Gold Minerals in Placers of the Anabar River in the Northeast of the Siberian Platform

Abstract

Areal placers of diamond and precious metals (platinum and gold) of unknown origin are widespread in the Anabar River basin on the northeastern part of the Siberian Platform. This article discusses the typomorphic features of palladium gold (porpezite) and ferroan platinum, which, in addition to fragmented individual grains, sometimes form close growths, which indicates their obvious genetic relationship. This can be used to delimit the primary sources of commercial components of complex placers by their genetic types. The composition of minerals was determined on a Camebax-Micro (Cameca, France) microprobe analyzer, and their microstructural relationships were studied using the scanning microscope JSM-6480LV JEOL. Determination of the structure and parameters of elementary lattices of minerals was carried out on the D8 Discover diffractometer. According to microprobe analysis, the Pd content in porpezite ranges from 0.73% to 12.83%, Ag does not exceed 2.75% and Cu reaches 3–4%. Considering the composition, such a gold–platinum mineral association from placers of the Anabar river is close to precious metals from placers of the Gulinsky massif, as well as Au–PGE ore occurrences related to ultramafic–mafic intrusions of other regions of the world. Complex gold–platinum-metal mineralizations are usually closely related to parent rocks and are often observed in sulfide and chromite ores of layered ultramafic–mafic intrusions with complex metasomatic and hydrothermal transformations. It is shown that in such cases gold and platinum form a magmatogenic paragenesis of minerals that coexist until the separation of hydrothermal solutions from magma, which, as a rule, transports Au and Ag with a small fraction of PGE from the fluid-ore-magmatic system in accordance with the model of the formation of gold–porphyry deposits. Within the Anabar diamond-bearing region, according to modern geophysical data, a significant number of local gravimagnetic anomalies associated with the presence of intrusive massifs of basic and alkaline-ultrabasic rocks in the cover and within the basement have been identified. This allows us to assume that the buried parent rocks of the Anabar Au–Pt placers may be located in both the Precambrian and Phanerozoic strata.

Formation of Intergrowths of Platinum-Group Minerals and Gold from Magmatogenic Ores in Relation to Phase Changes in Pt-Pd-Fe-Cu-Au System

“…The methods of collecting samples containing gold and platinum from placers of the Anabar River basin were described in our previous article [7], with their location shown in Figure 1. Gold and PGMs were studied in concentrates of heavy minerals obtained from dumps during the mining of diamond-bearing placers of the Mayat, Ebelyakh, Khara-Mas, and other rivers, where large (up to 3-8 mm in size) grains of precious metals and their intergrowths are often found.…”

“…Early in their article [7], the authors provided a mineralogical description of the association of platinum and palladium gold from placers of the Anabar River basin; it was shown that these noble metals develop magmatic paragenesis of minerals associated with complexes of alkaline ultramafic-mafic intrusions. Here, based on the characteristics of the chemical composition, as well as morphological and microstructural forms of intergrowth of PGM and gold, we try to test their interpretation regarding the origin of these minerals at the high-temperature magmatic stage of the formation of mafic intrusions.…”

“…These placers are recognized over vast territories (Figure 1) of the Lena-Anabar interfluve [1][2][3][4][5][6]; however, uncertainty remains about their sources. In [7], we examined the typomorphic features of palladium gold (porpezite) and ferroan platinum, which form intergrowths, thus indicating their evident genetic relationship. This approach can be applied to delineate the sources of valuable components of complex placers by their genetic types.…”

Editorial for the Special Issue “Native Gold as a Specific Indicator Mineral for Gold Deposits”

“…Several articles focus on the typomorphic features and sources of native gold placer deposits [12][13][14][15][16][17][18][19]. Becerra et al [12] studied the morphology, composition, and mineral inclusions in native gold from terraced placers in the Pureo Area (Southern Chile).…”

“…Okrugin and Gerasimov [16] studied palladian gold and platinum minerals in placers of diamonds and precious metals, widespread in the Anabar River basin on the northeastern part of the Siberian Platform, Russia. The composition of palladian gold, ferroan platinum, and other associated minerals and their microstructural relationships indicate a paragenetic connection between native gold and platinum group minerals.…”