Sulphur 硫磺 and salpetre 硝
Sulphur is a soft yellow mineral that easily ignites. It occurs naturally and has been 
known since antiquity and probably before. For many centuries, its main uses are as a bleaching agent and as a medical substance. It appears that elementary sulphur deposits are limited in China. By the 3rd century BCE, a process was developed to extract sulphur from pyrite (FeS2, commonly called fool’s gold). This involved the roasting of the mineral to produce iron and sulphur oxide. The sulphur oxide was then heated again in a reducing environment to produce elementary sulphur. The mineral thus was rarely mined but required firing technologies closely related to smelting.
Salpetre (nitre) is a white substance that looks like salt, and reacts explosive with reducing agents. It was known early and used mainly as a medical substance. The nature of the early source of the mineral is uncertain. Salpetre in the southwest was harvested in caves. As in other regions, these saltpetre crusts presumably derived from bat guano deposited over long periods. To purify the substance, it was soaked and cooked (ao xiao 熬硝) until the salpetre crystals remained in the pan. Extraction technologies of saltpetre were related to the treatment of salt brine.
Alchemists experimented with ignition and, in about the 7th century, found a formula of salpetre, charcoal and sulphur that caused explosions. Early experiments mainly led to fires and probably to lost fingers as well. By the 10th century, the new fire medicine huoyao 火药 (black gunpowder) acquired military uses. Saltpetre and sulphur suddenly acquired a new importance. Procurement, especially of saltpetre, became an issue, and so did their control. In a society that had long disarmed its population, any production or use of substances that could be used for armament outside the defined government uses was prohibited.
Mining history in the Far Southwest and the borderlands
Salpetre caves were exploited in the Chongqing 重庆 area, in Guizhou 贵州 and Yunnan 云南. The mineral is explicitly listed as a resource produced in Yunnan in the Yuan 元 History (Yang Shouchuan 2014, 47). The Ming 明 and Qing 清 states banned all exploitation of substances with potential military uses, especially of explosives. This appears to have been effective, as their subjects in fact rarely carried weapons of any sort. At the same time, however, the frequent use of firecrackers for festive and ritual events strongly suggests that the control was less pervasive than the regulations suggest.
This situation is reflected in a considerable number of place names that suggest sulphur and saltpetre exploitation despite the fact that no known registered sites existed and that all military substances were banned in borderland regions.
We have encountered historic saltpetre mine in a small side valley of the Jinshajiang 金沙江 in Heqing 鹤庆 that has several small copper mines, and sulphur extraction facilities at a site where some silver and iron exploitation took place in the past. Neither site could be dated. As exploitation was before living memory of the local village, it can be dated to before 1920 with some certainty, and possibly to before 1850.
The minerals are beyond the scope of this project. They are considered as loosely related activities in mineral exploitation that might occur in the vicinity or even on the same sites of metal mining.
