Laodonggou Mine, Ejin Banner (Ejina Co.), Alxa League (Alashan Prefecture), Inner Mongolia, Chinai

Regional Level Types
Laodonggou Mine	Mine
Ejin Banner (Ejina Co.)	County
Alxa League (Alashan Prefecture)	Prefecture
Inner Mongolia	Autonomous Region
China	Country

Oxidized-leaching type gold deposit, consisting of pervasively oxidized gold-bearing polymetallic sulfide veins in fracture zones of a dolomite marble around diorite porphyry dykes. The oxidation zone extends to great depths and the ore mainly consists of secondary arsenate minerals containing visible gold and silver. Except for residual galena, the primary sulfide minerals only occur in microscopic quantities.

Gold resources of 6.76 tons with an average grade of 5.83 g/t, as well as 68,747 tons of silver, 12,216 tons of lead, 11,424 tons of copper, and 15,120 tons of arsenic. The Laodonggou deposit hosts various ore types, including hydrothermal vein-type ore bodies, skarn-type ore bodies, and “karst cave-type” oxidized ore bodies. The mineralization process is complex, having undergone multiple stages of skarn and middle-low temperature hydrothermal mineralization. The skarn mineralization stage is particularly important, with garnet being the most significant alteration mineral.
The ore body Ⅰ is mainly controlled by the X-shaped faults assemblage formed by the intersection of nearly EW and NW faults. Ore body Ⅱ is controlled by the Y-shaped fault assemblage consisting of NWW and NW faults. The nearly EW faults influence the distribution of the skarn and ore body Ⅲ. Ore body Ⅳ is mainly constrained by NWW faults, while NW faults dictate the occurrence of ore body Ⅴ. The largest ore body extends up to 400 m in length, with thicknesses ranging from 0.65 to 15.54 m and Au grades of 0.38–31.40 g/t, occurring at elevations between 996 and 1311 m. Based on associated minerals, the ore bodies are classified into gold–silver–lead and gold–silver–copper types. For example, ore body I-1 has Au grades of 0.51–12.85 g/t, Ag grades of 44.55–70.38 g/t, and Pb grades of 0.51–4.89 %. Ore body III-1 contains Au grades of 0.55–3.98 g/t, with Ag grades of 2.12–9.94 g/t and Cu grades of 0.10–0.47 %. Ore body IV-1 has Au grades of 0.72–3.53 g/t and Pb grades of 0.61–2.14 %.
1. Prograde skarn stage: Dominated by garnet, diopside, and tremolite
2. Retrograde skarn stage: Characterized by magnetite, pyrite, chalcopyrite, and bornite, along with gangue minerals such as epidote, chlorite, serpentine, quartz, and calcite. Alteration types include skarnification, sericitization, and serpentinization
3. Hydrothermal quartz–sulfide stage: Composed mainly of pyrite, galena, arsenopyrite, sphalerite, and quartz
4. Hydrothermal quartz–sulfide–carbonate stage: Dominated by pyrite, galena, arsenopyrite, chalcopyrite, sphalerite, quartz, and calcite
5. Surficial oxidation stage: Affects mineral bodies within 200–300 m below the surface, leading to varying degrees of oxidation. This stage results in the formation of secondary minerals such as hematite, limonite, jarosite, azurite, malachite, and various arsenate minerals, including olivenite, lead arsenate, zinc arsenate, and hydroxyl-borneite.

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References