Sodic-Calcic Family of Alteration in Porphyry Systems of Arizona and Adjacent New Mexico

Abstract

Sodic-calcic alteration has affected numerous districts with Laramide porphyry systems 22 across Arizona and New Mexico. Previously undocumented Na-Ca alteration has been identified 23 at Charleston, Sycamore Canyon, Silver Bell, and the Ninetysix Hills in Arizona and the Central 24 mining district in New Mexico. These new occurrences are compared to sodic-calcic alteration at 25 the Sierrita-Esperanza deposit (Pima district), Ajo mining district, Tea Cup pluton (Kelvin-26 Riverside district), and the Eagle Pass dike swarm in Arizona. 27 Spatial positions, crosscutting relationships, and mineral assemblages and compositions 28 allow for interpretation of the geochemical conditions of formation and implications for 29 associated hydrothermal processes. Diopside-or andradite-grossular solid solution (Ad68-Ad72) -30 stable assemblages representative of calcic alteration typically occur in deep and/or distal 31 positions but are less commonly exposed. The sodic-calcic and sodic alteration types, however, 32 occur more proximal to the porphyry orebody. Sodic-calcic assemblages containing Na-33 plagioclase (An10-An33) -Ca-amphibole ± epidote are focused along granite cupolas near the 34 base of orebodies, and these grade into shallower sodic assemblages containing albite (An00-35 An09)epidotechlorite. Mineral composition and fluid inclusion data suggest that Na-Ca 36 plagioclase-bearing assemblages form at higher temperatures (360-470°C+) than later, lower 37 temperature albiteepidote assemblages (>250°C). Calculated δD isotopic compositions of 38 fluids in equilibrium with Na-Ca alteration minerals span a broad range (-46 to -1‰) and are 39 consistently less negative than magmatic fluids. Where members of the Na-Ca family of 40 alteration assemblages are present in porphyry systems, many lines of evidenceincluding 41 isotopic compositions of minerals and the geologic alteration zoning patternsare consistent 42 with an origin by incursion of saline external fluids. 43 Where Na-Ca alteration is present, it is best developed at relatively deep levels of 44 3 porphyry systems. Several Laramide systems that are well exposed at comparably deep levels 45 lack Na-Ca alteration, probably because sources of saline fluid were absent or hydrologic 46 conditions were unfavorable for the incursion of saline external fluids. Though similar in 47 temperatures, isotopic compositions, mineral assemblages, and zoning patterns, Na-Ca alteration 48 in Laramide systems is volumetrically smaller than in Jurassic systems documented in the 49 western United States, probably because saline external fluids were much less abundant during 50the Laramide after a tectonically-driven excursion in paleoclimate from arid to humid conditions. 51 phases of a batholith, whereas variably developed iron oxide-rich alteration in porphyry districts 69 commonly is distal to and at shallower levels than the porphyry intrusions (Carten, 1986; Dilles 70

Applications and Limitations of Elastic Thermobarometry: Insights From Elastic Modeling of Inclusion‐Host Pairs and Example Case Studies

“…We focus on testing the ab-in-ep barometer because epidote is a "stiff" host and is abundant in many mafic and felsic metamorphic rocks. Albite and epidote are also common in a wide variety of hydrothermal systems, and the ab-in-ep barometer can be useful for constraining pressures of deep roots below porphyry deposits, where both minerals are commonly found as alteration products (e.g., Runyon et al, 2019).…”

Mineralogical Constraints on the Potassic and Sodic-Calcic Hydrothermal Alteration and Vein-Type Mineralization of the Maronia Porphyry Cu-Mo ± Re ± Au Deposit in NE Greece

“…The sodic-calcic alteration typically postdates potassic alteration [2,19], but in Maronia, these two types of alterations are possibly contemporaneous, since there is not any clear evidence for the relative age from their distinctive mineral assemblages. Both alteration assemblages overprint each other, and secondary biotite, K-feldspar, magnetite and rutile of the potassic alteration coexist with hydrothermal actinolite, sodic-calcic plagioclase (albite/oligoclase/andesine) and titanite of the sodic-calcic alteration.…”

“…The study aims to understand the association of the early high temperature alterations and the evolution of the porphyry system in one of the most promising metallogenic belts of south-eastern Europe, spatially associated with the Rhodope massif. Identification of potassic and sodic-calcic hydrothermal alteration zones may provide useful exploration vectors as they may point toward undiscovered parts of the deposits [18,19]. Based on field observations and a mineralogical study, we prepared new geological and hydrothermal alteration maps from pre-existing geological maps of the area [11], complemented by new field observations and mineralogical analyses.…”