Summary:
A total of 18 gold mineralization domains were defined, where two sub-zones were named as NE zone and SW zone, covering NE open pit and SW open pit, respectively. NE zone accounts for 78% of the total mineral resources of the CSH gold deposit, whereas the SW zone occupies only 22%.
Gold mineralization domain N1
The largest gold domain at the cross-section of exploration line 8,800 to 11,100 was defined in the CSH deposit area, with an irregular tabular shape, controlled by bedding-like shear structures. The mineralized domain is entirely hosted in the Second Member of the Bilute Formation, Mesoproterozoic Bayan Obo Group, with most parts outcropping at the surface. It strikes NE 55°–65° overall, plunging NW at a dip of 70–85°. A total of 645 diamond drill holes on a grid of 50–100 m (strike) by 50–100 m (plunge) have delineated the domain over a strike length of 2,346 m and a plunge extension of 1,100–1,540 m, with a horizontal thickness of 70–400 m. The elevation of the domain ranges from 1,677 m to 230 m ASL. Domain N1, accounting for about 76.5% of the total mineral resources of the CSH Gold Deposit, is dominated by gold mineralization grading 0.57 g/t Au.
Gold mineralization domain W1
The second largest gold domain at the cross-section of exploration line 6,700 to 9,100 was defined in the CSH gold deposit area, with a strata-bound shape controlled by bedding shear structures. The mineralized domain is entirely hosted in the Second Member of the Bilute Formation, Mesoproterozoic Bayan Obo Group, with most parts outcropping at the surface. One post-mineralization fault offsets the mineralized zone between exploration lines 7,300 and 7,500. It strikes NE 65°–70° overall, plunging NW with a dip of 85–90°. A total of 277 diamond drill holes on a grid of 25–100 m (strike) by 25–100 m (plunge) have delineated the domain over a strike length of 2,400 m and a plunge extension of 610–750 m, with a horizontal thickness of 90–116 m. The elevation of the domain ranges from 1,655 m to 905 m ASL. Domain W1 accounts for about 21.6% of the total mineral resources of the CSH Gold Deposit and is dominated by gold mineralization grading 0.56 g/t Au.
The metallic minerals are mainly composed of pyrrhotite and pyrite with minor chalcopyrite, sphalerite, galena, arsenopyrite, native gold, and electrum. Gangue minerals consist of quartz, mica group, and feldspar, with minor calcite, diopside, tremolite, and apatite. Statistical data indicate that about 74% of gold occurs in interstices among sulfides and gangue minerals, or is hosted in fissures of various minerals, implying that most gold is easy to recover.
The mineralization texture matches that of the original rocks in most mineralized material, with sparsely disseminated sulfides and local stockwork quartz or pyrite veinlets. Statistical data show that more than 50% of sulfide grains are smaller than 0.074 mm (200 mesh). Gold minerals include native gold and electrum, appearing in irregular shapes with 8.42% larger than 200 mesh. Gold minerals usually occur with various sulfides, and high-grade mineralization is always associated with stockwork quartz and pyrite veinlets.
The characteristics of the gold mineralization at the CSH deposit are summarized as follows:
• The CSH gold deposit is a low-grade but large-sized deposit. Tectonically, it is located on the northern edge of the North China Platform, which was uplifted to a continental environment after the Hercynian orogeny in the Permian Period and is characterized by intense magmatic intrusions. This tectonic setting differs from that of the Muruntau or Sawaya’erdun gold deposits in the Tianshan-Mongolia Hercynian fold belt in China.
• Gold mineralization is hosted in low-grade metamorphic rocks of the Mesoproterozoic Bayan Obo Group, controlled by a brittle–ductile shear zone assumed to have formed during the Hercynian orogeny. Various dykes (lamprophyre, diabase, diorite, aplite, pegmatite) and quartz veins developed along the structure. Gold mineralization formed later, under intense shear conditions. Alteration is generally weak, but coarse gold is commonly associated with stockwork quartz and pyrite veinlets.
• Microscopic studies and testing show that mineralization is dominated by native gold and electrum, with minor visible gold and low-grade silver (less than 2 g/t). Fine-grained pyrite is scarce (~0.26%). Both oxidized and primary ores are amenable to heap leaching.
It is concluded that the CSH gold deposit represents an orogenic-style gold system, hosted in Mesoproterozoic low-grade metamorphic rocks and characterized by low-grade but large-tonnage mineralization.