Chemical and isotopic evolution of hydrothermal solutions at Bingham, Utah

Abstract

Systematic changes in mineral assemblages, mineral compositions, fluid inclusion characteristics, and hydrogen and oxygen isotope compositions in altered igneous rocks in the Bingham, Utah, porphyry copper deposit record the chemical and isotopic evolution of the hydrothermal solutions. Hydrothermal alteration in and surrounding the Bingham porphyry copper deposit consists of an outer propylitic zone of chlorite, epidote, and actinolite; a transition zone of hydrothermal biotite, actinolite, epidote, and chlorite; and an inner potassic zone of hydrothermal biotite and K-feldspar. Later sericitic and argillic alteration are superimposed on early potassic and propylitic alteration. Compositions of alteration minerals determined by electron microprobe methods are: biotite, mole fraction phlogopite (Mg/Mg + Fe) 0.58 to 0.83; actinolite, mole fraction tremolite (Mg/ Mg + Fe) 0.58 to 0.79; epidote, mole fraction pistacite (Fe/Fe + A1) 0.27 to 0.30; and chlorite, mole fraction clinochlore (Mg/Mg q-Fe) 0.66 to 0.76. Mineral compositions, especially MnO and MgO in chlorite, MnO in epidote, and TiO2 in biotite, vary systematically with distance from disseminated ore. MgO in chlorite increases from 20.6 to 24.6 wt percent. MnO in chlorite and vein epidote increases from less than 0.1 to 0.59 wt percent and from 0.08 to 0.73 wt percent, respectively. The average mole proportion Ti in biotite increases from 0.1 to 0.24.Temperatures and salinities from fluid inclusions range from greater than 600øC and 50 equiv wt percent NaC1 for the potassic zone to approximately 370øC and 33 wt percent for the propylitic zone. Coexisting liquid-rich and vapor-rich inclusions which homogenize at temperatures similar to the liquid and vapor phase, respectively, suggest boiling from the potassic core out to the potassic-propylitic transition zone. Compositions and homogenization temperatures for fluid inclusions suggest average P•//-T conditions which vary smoothly from the potassic core to the propylitic fringe: 600øC and 800 bars for the potassic zone, 450øC and 500 bars for the transition zone, and 350øC and 200 bars for the outer propylitic zone.Thermochemical calculations show that log faro decreases from 2.74 in the potassic core to 2.17 in the propylitic zone fringe, logfsa decreases from -1 to -3.3 in the core to -8.7 in the propylitic zone, and log foa decreases from -16 to -17.5 in the core to -29 in the same interval. The log activity ratios of Ca, Mg, and K to hydrogen ion increase from the potassic to the propylitic zone. K+/H + increases from 3.1 to 3.4, Mg+2/(H+) a increases from -2.25 to 4.25, and Ca+2/(H+) a increases from less than i to 7.75.The extent of oxygen isotope exchange between the hydrothermal vein fluids and the igneous rock matrix in the Bingham stock increases with increasing temperature, abundance of alteration and quartz veins, thickness of veins, and fracture intensity. All these parameters generally increase inward from the propylitic zone into the core of the potassic zone. Within the potassic zone, there is...

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“…Then, influx of meteoric water caused the dissolution of early-formed copper sulfides, resulting in remobilization of Cu-Mo into the silicic veins. [45][46][47] Casino (Selby and Nesbitt, 2000) [11] , Miduk (Boomeri et al, 2009), Sarcheshmeh (Boomeri et al, 2010) [48] , Los Pelambres (Taylor, 1983) [41] and Santa Rita (Jacobs and Parry, 1979) [49] . Similar symbols as in Figure 4.…”

Direct Associations Between Potassic Igneous Rocks and Gold-Copper Deposits in Volcanic Arcs

“…6.24) is located about 32 km southwest of Salt Lake City, in the central Oquirrh Mountains, Utah (Bowman et al 1987;Waite et al 1997). With a production of 1300 million tonnes of 0.85 wt% copper ore from 1904 to 1976, the Bingham mining district represents the largest porphyry copper deposit of North Major elements are in wt%, and trace elements are in ppm.…”

Chemistry of magmatic and alteration minerals in the Chahfiruzeh porphyry copper deposit, south Iran: implications for the evolution of the magmas and physicochemical conditions of the ore fluids

“…Data for other intrusions: Bingham (Lanier et al, 1978;Parry et al, 1978;Bowman et al, 1987), Casino (Selby and Nesbitt, 2000), Miduk (Boomeri et al, 2009), Sarcheshmeh (Boomeri et al, 2010), Los Pelambres (Taylor, 1983, and Santa Rita (Jacobs and Parry, 1979). , 1978;Parry et al, 1978;Bowman et al, 1987), Casino (Selby and Nesbitt, 2000), Dalli (Ayati et al, 2008), Miduk (Boomeri et al, 2009), Sarcheshmeh (Boomeri et al, 2010), Duolong (Li et al, 2011), and Batu Hijau (Idrus et al, 2007). continental crustal source components by such processes as partial melting, magma mixing, and assimilation. I-type granitoids containing biotite with log (X Mg /X Fe ) > -0.21 have been divided by Brimhall and Crerar (1987) into 3 subgroups based upon increasing F/OH ratios (Figure 10).…”