The common occurrence of cinnabar and stibnite in well-defined districts in the same epithermal environments suggests that similar physiochemical processes are responsible for the genesis of the two minerals; however, cinnabar and stibnite tend to be segregated within these districts and also within individual deposits that contain both minerals. Where cinnabar and stibnite occur in contact, textural evidence indicates that cinnabar is generally younger, although some textures suggest overlap of deposition. To better understand the physicochemical processes involved in the formation of cinnabar and stibnite deposits, we investigated the solubilities of cinnabar and stibnite in aqueous Na2S solutions that were simultaneously saturated with both cinnabar and stibnite at concentrations from 0.384 percent (0.0492 mol/kg) to 1.772 percent(0.227 mol/kg)Na2S at temperatures from 150° to 250°C, at 100 bars pressure. The ratio of dissolved Sb2 S3 to HgS under most conditions is larger than 25:1 moles per mole. We conclude that alkaline sulfide solutions could not transport geologically appreciable amounts of HgS while they are saturated with stibnite; major amounts of HgS could only be transported in solutions that are undersaturated with stibnite. Solubility behavior of HgS and Sb2 S3 is thus a possible mechanism for the segregation of cinnabar and stibnite, especially when the conduit system is modified during the episode of mineralization. The deposition of stibnite before that of cinnabar in most places but with minor overlapping deposition in some places is in accord with deductions made from the solubility studies.
|Title||Equilibria of cinnabar, stibnite, and saturated solutions in the system HgS-Sb2S3-Na2S-H2O from 150° to 250°C at 100 bars, with implications concerning ore genesis|
|Authors||R. E. Learned, G. Tunell, F. W. Dickson|
|Publication Subtype||Journal Article|
|Series Title||Journal of Research of the U.S. Geological Survey|
|Record Source||USGS Publications Warehouse|