SUBSURFACE BRINES AND MINERAL EQUILIBRIA

Approximately 2,500 analyses of brines are classified as to rock type (limestone, sandstone, dolomite, granite wash, evaporite, shale). The raw data are subjected to factor analysis to determine possible kinds of mineral equilibria; conclusions from factor analysis data are used to calculate ion products which are compared with equilibrium values. The majority of analyses are incomplete relative to a critical equilibria analysis. Normally Cl, SO4, Na, Ca, Mg, HCO3 and Sr/1bBa are reported. In this context: (1) most waters regardless of rock type are basically Na, Ca chloride (ion exchange?) with a secondary inverse relationship to HCO3 (CaCO3 saturation); (2) most waters show SO4 to be an independent variable (with a weak inverse relationship to HCO3, a positive correlation to Mg, and sometimes an inverse relationship to Sr, Ba suggesting Sr, Ba/1bSO4 equilibrium); (3) Ca and Mg show a stronger inverse correlation to HCO3 in dolomite than in other rock types; (4) Ca shows a stronger correlation with Mg in dolomite than limestone (suggesting Ba, Sr/1bCO3 equilibrium). Conclusions from a smaller population of more complete data confirm the above and suggest in addition an equilibrium involving K/1bMg/1bH/1bSi. © 1969.