Antimony Deposit Types & Origins
Most Sb deposits are formed by hydrothermal solutions at low temperatures and shallow depths, giving rise to filled fissures, joints, and rock pores and to irregular replacement deposits. Some primary deposits have been enriched in oxidized products through residual weathering.
China, a main producer with Sb deposits occurring in deformed Silurian sandstone in veins seams, pockets and lenses, with the richest deposits located beneath anticlinal structures. The ore grades about 6% and is hand sorted to 60%. Two principal kinds of Sb deposits are mined: stibnite-quartz veins in clastic host rocks, and stibnite-galena-arsenopyrite replacement deposits in carbonate rocks, the former being the dominant ore mined in the country. In the Wushih deposits, stibnite is associated with Au-bearing quartz grading 0.20-0.25 oz/ton. These were originally mined for the gold content, and the stibnite was discarded as waste. At depth, the shoots contract sharply and stibnite gives way to pyrite.
The Hsi-K’uang-Shan district in central Hunan contains the richest and largest structure in the entire region. Gently folded dolomitic limestone and few beds of shale, sandstone, and low-grade bituminous coal overlie a quartzitic sandstone that contains the deposit. The ore bodies are concentrated along the crest of a gentle anticline whose folding caused jointing and brecciation in the brittle quartzites that were sandwiched between shales. The most favourable bed for ore is a quartzite along the up thrown side of a prominent fault. In places, stibnite is oxidized to stibiconite and contains less than 1% of combined As, Pb and Cu.
Worldwide sources include:
- Mexico – Deposits occurring in veins in limestones intruded by porphyry.
- Bolivia – Large reserves in the antimony belt, with high grade deposits in shallow quartz veins in Palaeozoic shales (stibnite-base metals sulphides association).
- Algeria – A mineralized belt across Algeria from Morocco to Tunis contains antimony veins in limestone.