Applications of the reaction progress variable to hydrothermal alteration associated with the deposition of the Questa molybdenite deposit, NM

This study demonstrates a technique that quantitatively represents 'recognizable alteration' for ore exploration and development. It is the first study that has modelled geochemistry in terms of the proportion of 'recognizable' rock alteration suites. The quantities ;The advantages of this method are: (1) It employs data currently gathered by the exploration geologist: whole-rock and trace element geochemistry, identification of 'recognizable' rock alteration suites, paragenetic and petrographic analysis of thin sections, and electron microprobe analyses. (2) The method assigns measurable quantities to rock, so that different alteration mineral assemblages may be compared and lithologic differences between model and prospect become accountable. (3) The thermodynamic and mass balance calculations may all be computer coded and first hand knowledge of classical thermodynamics is not necessary. (4) The costs of retrieval of mineral compositions is relatively small, on the order of whole-rock and trace element geochemistry per sample. (5) In conjunction with studies of the same type of hydrothermal systems, an energy and/or F/R 'yardstick' could become an indicator as to the potential grade of a prospect's alteration suite when compared to a quantified model.;The disadvantages to this procedure are: (1) Inhomogeneties in the country rock may mask the exact protolith for a given sample, so that a empirically derived precursor would be necessary. (2) In order for this technique to be truly effective, a good knowledge of the alteration paragenesis is necessary. To generate a 'ore grade-alteration' yardstick would require data from accessible deposits and nearly economic prospects. (3) The largest errors in the calculation of energy budget and fluid-rock ratios may be those of both the type of country rock and any inhomogeneties in the host rock. (Abstract shortened with permission of author.).