The Sin Quyen Cu–Fe–Au–REE deposit is localized in the Proterozoic deposits of the Phan Xi Pang zone, northern Vietnam. The mineralization is formed by lenticular and sheet-like bodies occurring concordantly with the host rocks. Seventeen orebodies have been recognized in the deposit, which form an ore horizon up to 140 m in total thickness, about 2 km in strike, and up to 350 m in dip. The ores are of simple mineral composition: Au-rich copper and iron sulfides (chalcopyrite, pyrite, pyrrhotite) and iron oxides (magnetite, hematite). Gold and silver are distributed unevenly in the ores: Their contents vary from hundredths and tenths of ppm to 1.8 ppm. Copper sulfide ores are the main concentrator of gold and silver. All ores are characterized by high REE contents, tens and hundreds of times exceeding the element clarkes. The highest contents have been revealed for Ce and La. Orthite is the main carrier of REE. No correlation between REE and ore elements of sulfide-oxide ores has been revealed, which points to the independent formation of the mineralization. Orebodies together with the host rocks underwent metamorphism at 500–600 to 630–685 °C and 3–7 kbar. The spatial association of the mineralization with amphibolites (metamorphosed basites) and the mineral composition of ores suggest that the Sin Quyen deposit is of Cyprian volcanogenic type.

We present the results of a study of the geologic structure and age sequence of formation of the Late Neoproterozoic–Early Paleozoic plagiogranitoid and gabbroid associations in the Bumbat-Hairhan intrusive area of the Lake Zone in Western Mongolia. The petrogeochemical characteristics of the plagiogranitoids provide information about the conditions of formation of their parental melts at the island-arc and accretion–collision stages of the regional evolution. They also help to establish the main magma-generating sources as well as the major mechanisms of large-scale formation of granitoid melts and their relationship with ore generation processes. According to the trace-element and REE patterns and indicative ratios of these elements, the plagiogranitoids are subdivided into high- and low-alumina ones. Among the island-arc plagiogranitoids (551–524 Ma) of the Bumbat-Hairhan area, high-alumina varieties are the most widespread. They resulted from the partial melting of metabasites in equilibrium with garnet-containing restite at ≥ 15 kbar during their subsidence into the subduction zone. In geochemical features these plagiogranitoids are similar to high-Si adakites of different world regions. Island-arc low-alumina plagiogranitoids are scarcer. Their geochemical characteristics indicate that the parental melts were generated through the partial melting of metabasites in the lower part and/or in the basement of the island-arc system in equilibrium with amphibole-containing restite at ≤ 8 kbar. Plagiogranitoid associations of the accretion–collision stage (511–468 Ma) are the most widespread in the Bumbat-Hairhan area. They are subdivided into high- and low-alumina ones. According to the contents of trace elements and their indicative ratios, the low-alumina plagiogranitoids resulted from the partial melting of metabasites in equilibrium with plagioclase-containing restite at ≤ 8 kbar in the upper part of the collisional structure, and the high-alumina ones were generated through the melting of metabasites in the basement of thick crust in equilibrium with garnet-containing restite at ≥ 15 kbar. Geochronological studies in the Bumbat-Hairhan area revealed two stages of ore-generating processes spatially and temporally related to the formation of low-alumina plagiogranitoids. The early stage (518 ± 5 Ma), development of vein Cu (Au) mineralization, coincided in time with the formation of island-arc low-alumina plagiogranitoids of the Darbi massif (~ 524 Ma). The late stage (456 ± 4 Ma), formation of porphyry Cu-Mo (Au) mineralization, was synchronous with the formation of the low-alumina plagiogranites at the accretion-collision stage (~ 468 Ma).

Contents of major impurities (Ag, Cu, and Hg) have been studied in gold from ore deposits of various types: (1) associated with skarns and black shales (Altai–Sayan folded area (ASFA) and North Vietnam), (2) pluton-related porphyry Cu–Mo (ASFA), and (3) volcanic pyritic (Rudny Altai, the Urals, and North Vietnam). Analysis of gold ore mineralization in deposits of these types reveals diverse gold compositions along with diverse compositions of productive mineral assemblages. Silver is the most abundant impurity in gold from all fields studied, but its contents vary broadly even within a field type. The content of silver in gold depends not only on its abundance in hydrothermal solutions but also on other independent solution parameters: sulfur fugacity, temperature, salt composition, and pH. The regular decrease in native gold fineness from early to late generations in sulfide ore deposits is related to temperature decrease and large-scale sulfide formation. These processes reduce sulfur fugacity in the solutions and favor silver deposition in native gold rather than in sulfides. Gold of later generations is enriched in mercury in many deposits studied, whereas copper gravitates to earlier, high-temperature ones. In addition to deposition temperature, the contents of copper in gold are determined by its content in hydrothermal solutions, as evidenced by the association of copper-rich gold with basic–ultrabasic, skarn, and porphyry copper deposits. The processes causing the deposition of gold of various chemical compositions are complex. They correlate, to an extent, with gold mineralization temperature, whereas the spectrum of impurities often depends on the belonging of a gold deposit to a certain igneous complex.