NEW MINERAL OCCURRENCES FROM THE WUDA COALFIELD FIRES OF INNER MONGOLIA

The Wuda coalfield occupies a north-south trending syncline in the Helan Mountains of Inner Mongolia. Three major mines there, Wuhushan, Suhaitu, and Huangbaici, in addition to about 400 smaller ones supply China’s industrial base with coking coal. Approximately 9% of the coalfield is engulfed in surface and underground fires less than 100 m deep.

The sulfates godovikovite, zaherite, zincovoltaite, tschermigite, millosevichite, alunogen, and anhydrite, in addition to the halide salammoniac, and tectosilicate haüyne were found as condensation deposits encrusting quartzofeldspathic sand and sandstone adjacent to five surficial gas vents in the coalfield. With the exception of salammoniac, all minerals occur as separate phases within multi-phase cryptocrystalline masses.

These minerals, identified by X-ray diffraction, include the first identified association of zaherite, zincovoltaite, and haüyne with a coal fire, the first occurrence of godovikovite found outside of Russia and as a coal gas condensate, the second known occurrence of zincovoltaite besides Qinghai, China, and the third known occurrence of zaherite besides South Africa and Pakistan.

Scanning electron imagery suggests that godovikovite, zaherite, zincovoltaite, millosevichite, haüyne, and alunogen nucleated from a liquid subsequent to condensation of the liquid from coal fire gas, whereas salammoniac nucleated directly as a sublimation product of the gas. Textural evidence for the origin of anhydrite and tschermigite is concealed by quartz contamination.

Within four months of collecting, iron-magnesium sulfate rosettes nucleated on haüyne, zaherite, zincovoltaite, godovikovite, and alunogen stored in a sealed container at room temperature.

Complex exchange reactions involving coal gas, aqueous solutions, sediment, and rock during the migration of gas to the surface prior to exhalation and condensation, in addition to variations in coal bed chemistry, are likely responsible for the different mineral assemblages found at the five gas vents.

The chemistry of coal gas and its associated condensates is reflective of elements and compounds released as pollutants into soil, streams, ground water, and the atmosphere. Such pollutants may be responsible for a variety of environmental and human health problems including the destruction of floral and faunal habitats and skin and lung diseases.