ANALYSIS OF SECONDARY SULFATE MINERAL PARAGENESIS IN RELATION TO ENVIRONMENTAL CONDITIONS AND THE DECOMPOSITION OF SULFIDE MINERALS IN COAL

The formation of secondary sulfate minerals requires unique environmental conditions. The formation of these minerals within coal rely on the specific initial composition of the rock. The research consisted of three phases. Within the first phase, secondary sulfate mineral paragenesis was analyzed in a coal sample of unknown origin (found in an enclosed drawer among Slippery Rock University’s collection). The second phase included collection of environmental condition present during the formation of these minerals. The final stage used mineral and environmental constraints to understand the decomposition reactions of sulfide bearing materials within the sample.

The decomposed sediments were collected and analyzed through multiple methods such as petrographic analysis, laser induced breakdown spectroscopy, and scanning electron microscope imaging.

Identification of various secondary sulfate mineral (copiapite, melanterite, halotrichite, etc.) and the paragenetic sequence (pyrite decomposition) was achieved. This allowed for the reconstruction of environmental conditions, such as temperature, pressure, and humidity, present over the 40 years since the sample was initially stored in the sample draw. Elemental data indicates that carbon, iron, potassium, silicon, sulfur, and sodium, with nickel and strontium, along with other trace elements are present in the sample.

The mineral paragenesis was initiated by a potential flooding event of hot fluid or steam that penetrated the sample environment. These conditions encouraged both mineral growth and breakdown. The decomposition of pyrite was related to the sulfide oxidation through the introduction of water and oxygen. This resulted in the formation of the secondary sulfate minerals as well as sulfuric acid that stimulated the breakdown. The localized study area of the research presents insight to microenvironments that impact mineralogy and structural properties of samples.

Oxidation of sulfides in coal under unique conditions create specific mineralogical paragenesis, such as have been identified in this study. Further research into sulfide decomposition and secondary sulfate minerals may be conducted to understand properties of the decomposition and formation of minerals.