Gold Mineralization of the Gatsuurt Deposit in the North Khentei Gold Belt, Central Northern Mongolia

Abstract

Mineral assemblages, chemical compositions of ore minerals, wall rock alteration and fluid inclusions of the Gatsuurt gold deposit in the North Khentei gold belt of Mongolia were investigated to characterize the gold mineralization, and to clarify the genetic processes of the ore minerals. The gold mineralization of the deposit occurs in separate Central and Main zones, and is characterized by three ore types: (i) low-grade disseminated and stockwork ores; (ii) moderate-grade quartz vein ores; and (iii) high-grade silicified ores, with average Au contents of approximately 1, 3 and 5 g t −1 Au, respectively. The Au-rich quartz vein and silicified ore mineralization is surrounded by, or is included within, the disseminated and stockwork Au-mineralization region. The main ore minerals are pyrite (pyrite-I and pyrite-II) and arsenopyrite (arsenopyrite-I and arsenopyrite-II). Moderate amounts of galena, tetrahedrite-tennantite, sphalerite and chalcopyrite, and minor jamesonite, bournonite, boulangerite, geocronite, scheelite, geerite, native gold and zircon are associated. Abundances and grain sizes of the ore minerals are variable in ores with different host rocks. Small grains of native gold occur as fillings or at grain boundaries of pyrite, arsenopyrite, sphalerite, galena and tetrahedrite in the disseminated and stockwork ores and silicified ores, whereas visible native gold of variable size occurs in the quartz vein ores. The ore mineralization is associated with sericitic and siliceous alteration. The disseminated and stockwork mineralization is composed of four distinct stages characterized by crystallization of (i) pyrite-I + arsenopyrite-I, (ii) pyrite-II + arsenopyrite-II, (iii) galena + tetrahedrite + sphalerite + chalcopyrite + jamesonite + bournonite + scheelite, and iv) boulangerite + native gold, respectively. In the quartz vein ores, four crystallization stages are also recognized: (i) pyrite-I, (ii) pyrite-II + arsenopyrite + galena + Ag-rich tetrahedrite-tennantite + sphalerite + chalcopyrite + bournonite, (iii) geocronite + geerite + native gold, and (iv) native gold. Two mineralization stages in the silicified ores are characterized by (i) pyrite + arsenopyrite + tetrahedrite + chalcopyrite, and (ii) galena + sphalerite + native gold. Quartz in the disseminated and stockwork ores of the Main zone contains CO2-rich, halitebearing aqueous fluid inclusions with homogenization temperatures ranging from 194 to 327°C, whereas quartz in the disseminated and stockwork ores of the Central zone contains CO2-rich and aqueous fluid inclusions with homogenization temperatures ranging from 254 to 355°C. The textures of the ores, the mineral assemblages present, the mineralization sequences and the fluid inclusion data are consistent with orogenic classification for the Gatsuurt deposit.

Mineralogy of the Boroo Gold Deposit in the North Khentei Gold Belt, Central Northern Mongolia

“…Based on the present study on the Boroo and previous work on the Gatsuurt deposits by Khishgee et al (), the gold mineralization process in the NKGB can be generalized, because the Boroo and Gatsuurt deposits are the largest and representative resources among gold deposits in this belt (Cluer et al, ; Goldfarb et al, ; Khishgee et al, ). The Boroo and Gatsuurt deposits are situated in a similar geological setting, and are related to the major fault structure.…”

“…The occurrences of native gold in both deposits are also very similar to each other. Moreover, the estimated maximum mineralization temperature of 365 °C for pyrite‐II and arsenopyrite‐II in the disseminated and stockwork ores of the Boroo deposit is comparable with homogenization temperatures of up to 355 °C for fluid inclusions in quartz from the disseminated and stockwork ores in the Gatsuurt deposit (Khishgee et al, ). These are considered as common features of the gold mineralization in the NKGB.…”

“…In the case of lode gold deposits, the main resources are hosted in the Boroo (>54.1 Au tons), Gatsuurt (>50 Au tons), Ulaanbulag, Baavgait, Ereen, Sujigtei, Tsagaanchuluut, Urt and Kharganat deposits (Dejidmaa, ; Gerel et al, ) (Fig. ), which are classified as orogenic type (Cluer et al, ; Goldfarb et al, ; Khishgee et al, ). These gold deposits are similar to each other in terms of ore types.…”

“…Hendry et al () and Khishgee et al () studied all the above ore types in the Gatsuurt deposit, and grouped them into three ore types: (i) disseminated and stockwork type with low sulfide and gold contents; (ii) quartz vein type with low sulfide and high gold contents; and (iii) strongly silicified and brecciated type with low to moderate amounts of sulfides and high gold contents. Khishgee et al () suggested two main stages of ore mineralization, in which the disseminated and stockwork ores were formed from hydrothermal ore fluids in an early stage, and the quartz vein and silicified ores were emplaced in later stages.…”

Corrosion Behavior of a Pyrite and Arsenopyrite Galvanic Pair in the Presence of Sulfuric Acid, Ferric Ions and HQ0211 Bacterial Strain

“…The chemical formulas of pyrite and arsenopyrite are FeS 2 and FeAsS, respectively. Pyrite and arsenopyrite are the two most important gold-containing minerals in gold ores [1][2][3][4]. Fine-grained or submicroscopic gold is disseminated within pyrite and arsenopyrite, thereby rendering gold inaccessible to cyanide solutions [5].…”