Modes of occurrence of gold in the Xindigou gold deposit, Inner Mongolia

The Xindigou gold deposit in Inner Mongolia is a typical greenstone belt gold deposit. Microscope and scanning electron microscope were used to study the modes of occurrence of gold. 602 grains of native gold were recognized, including inclusion, fissure-filling, and intergranular and interlocking gold. The gold-hosting minerals are mainly pyrite and quartz, which account for 95% of the total gold-hosting minerals, and minor K-feldspar, sericite, siderite, limonite, tetrahedrite, sphalerite, galena were also identified. On the basis of statistics, the gold granularity is mainly characterized by micro extra particulate (0.2-5 μm), micro fine particulate (10-20 μm), microscopic medium (20-50 μm), and micro particulate (5-10 μm) grained gold, accounting for 32.23%, 26.91%, 20.6%, and 16.11%, respectively. The micro coarse-gained gold which was observed in the sample and under the microscope is relatively minor but plays an important role in the ore grade and total resource. Electron microprobe analysis and phase analysis show that gold occurs mainly as independent gold minerals. The gold minerals are mainly native gold and secondary electrum (the average fineness is 803), which indicates that gold was formed under the condition of medium temperature and depth.