| Description |
Forsterite (Fo) is developed extensively in dolomite marbles in the Alta, Utah contact aureole. Through the Fo zone and much of the periclase (Per) zone, the number of forsterite (Fo) crystals/mol Fo increases and the average Fo grain size decreases as the Alta Stock intrusive contact is approached. Excluding the innermost Per zone, ?18O (Carbonate-Fo) values increasingly depart from equilibrium values with increased metamorphic grade. These textural and oxygen isotope trends reflect progressively greater reaction affinity (Ar) driven by the combined effects of elevated temperatures, faster heating rates, and decreasing X(CO2) in infiltrating fluids toward the igneous contact. Significant variation exists in the number of Fo crystals/mol Fo, d18O (carbonate), and ?18O (Carbonate-Fo) between strata within individual outcrops at several locations. At most sites, the number of Fo crystals/mol Fo and d18O value of carbonate matrix are negatively correlated, suggesting that increased infiltration of low X(CO2) and low d18O fluid drives Ar higher. In the outer Fo zone, neither ?18O nor d18O (carbonate) correlate with Fo crystals/mol Fo values because infiltrating fluids have largely exchanged isotopically with the marble in this part of the aureole. A suite of trace elements were analyzed in samples from the Alta Stock, skarns, Alta aureole marbles, and the carbonate protolith. To detect concentration anomalies element concentrations are normalized to Al, which is demonstrated to be immobile in the marbles of the aureole. Positive concentration anomalies are documented for Ba, Cu, Pb, Zn, Sr, Rb, and K to varying distances from the intrusive contact. Fe and Mn anomalies are absent, suggesting that crystallizing skarn minerals effectively exhausted the Fe and Mn supply of infiltrating fluids before they reached significant distance in the aureole. Within the zone of 18O/16O depletion (< 400 m from the igneous contact), negative correlations are observed between concentrations and d18O (carbonate) for Cu, Pb, Zn, and Ba, suggesting a link between elevated fluid flux and the addition of these elements to the carbonate protolith. These results demonstrate that integrated isotopic and trace element data have potential applications in the exploration for skarn deposits and other intrusion-centered, carbonate-hosted metallic deposits. |
