Palladian Gold: Chemical Composition, Minerals in Association, and Physicochemical Conditions of Formation at Different Types of Gold Deposits

Abstract

This paper reviews and summarizes the available information on the composition of palladian gold with various contents and sets of isomorphic impurities (Ag, Cu, Hg) at 50 deposits and ore occurrences with Au-Pd mineralization. It is revealed that Palladian gold is represented by the systems Au–Pd, Au–Pd–Hg, Au–Pd–Cu, and Au–Pd–Ag–Hg, but more frequently corresponds to Au–Pd–Ag, Au–Pd–Ag–Cu, and Au–Pd–Ag–Cu–Hg. Objects with palladian gold belong to different types of gold deposits and to the deposits at which the main components of ores are PGE, Cr, Cu, Ni, V, and Ti. We propose a classification of the types of deposits with palladian gold: (1) PGE ore deposits related to mafic–ultramafic magmatic complexes (two subtypes—(a) low-sulfide-grade (less than 2%–5% sulfides) Alaskan, and (b) high-sulfide-grade (more than 5% sulfides) Norilsk); (2) orogenic gold deposits (OG); (3) epithermal (porphyry) gold–copper deposits (EPGC); (4) iron oxide copper gold deposits (IOCG); (5) ferruginous quartzite deposits; (6) volcanic exhalation; and (7) gold-PGE placers of five subtypes corresponding to the types of 1–5 primary sources. Palladian gold is mainly high-fineness (910‰–990‰), is less frequently medium-fineness, and contains Ag and Cu, but does not contain Hg at the deposits of types 1, 3, and 4. The only exception is the Au-Pd-Hg Itchayvayam ore occurrence (Kamchatka, Russia), for which two varieties of Pd,Hg-bearing native gold (fineness 816‰–960‰ and 580‰–660‰) are determined. Low-fineness palladian gold with the major content of Ag is typical of OGD deposits. Medium-fineness palladian gold occurs at ferruginous quartzite deposits and in volcanic exhalations. Hg, Ag, Cu-bearing high-fineness palladian gold is present mainly in placer deposits (type 7). The most common minerals in association with palladian gold are arsenides, stibioarsenides, sulfides, stannides, bismuthides, tellurides, and selenides of Pd and Pt. These are typical of deposit types 1 and 7. The minerals of Au, Ag, and Cu (tetra-auricupride, aurostibite, chalcopyrite, bornite, chalcocite, eucairite, etc.) are in association with palladian gold at OG, EPGC, and IOCG deposits. Hg minerals (cinnabar, tiemannite, coloradoite, potarite) are at some deposits (types 1, 2, 7-1, 7-4). Cu, Fe, and Pd oxides (tenorite, hematite, magnetite, PdO, (Pd,Cu)O) and Fe and Pd hydroxides (goethite, (Fe,Pd)OOH) occur at the deposits of the 3, 4, and 7 groups and indicate the highly oxidizing conditions of ore formation. The most common minerals among host minerals are quartz and muscovite, including fuchsite (Cr-Ms), chlorite, albite, K-feldspar, hornblende, and carbonates (calcite, siderite, etc.). The fineness, content, and set of impurities in palladian gold and minerals in association with it reflect the mineralogy of Au-Pd ores and allow them to be used as indicators for the deposit types.

Mineralogical Method as an Effective Way to Predict Gold Ore Types of Deposits in Platform Areas (East of the Siberian Platform)

“…Identified patterns made it possible to develop a method for predicting minerogenic types of gold deposits based on the indicators of placer gold and features of their distribution and to link them with various geological structures for the first time [15]. Similar studies on the mineralogy of placer gold, in order to identify the types of ore sources and the genesis of placers, have been successfully conducted and continue to be developed by Russian scientists [16][17][18][19][20][21][22] and also by foreign researchers [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] The study of the typomorphic features of placer gold (morphology, chemical composition, micro-inclusions, internal structure) in order to identify minerogenic types of ore sources was carried out using well-known mineralogical and geochemical methods. All analyses were performed in the laboratory of physical-chemical methods of analysis of the Diamond and Precious Metal Geology Institute, SB RAS (DPMGI SB RAS), Yakutsk (Russia).…”

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 Cu-Pd-Au diagram also shows two-phase areas at 350 and 550 • C surrounding the ordered phases of PdCu and AuCu, which according to [26] are in contact at 545 • C. Palladium alloying of gold-copper alloys increases the formation temperature of the AuCu compound. The article [44] describes in detail the associations of minerals of the Cu-Pd-Au system, their compositions, and conditions of formation in various types of gold deposits.…”

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

“…The review by Palyanova et al [11] summarized the available information on the palladian gold of several compositions and types of isomorphic impurities (Ag, Cu, Hg). The authors concluded that palladian gold more frequently corresponds to the Au-Pd-Ag, Au-Pd-Ag-Cu and Au-Pd-Ag-Cu-Hg systems and less often to Au-Pd, Au-Pd-Hg, Au-Pd-Cu, Au-Pd-Ag-Hg.…”