Fluid flow and the Heart Mountain fault: a stable isotopic, fluid inclusion, and geochronologic study

Abstract

Numerous studies have proposed that movement along the 3400-km 2 low-angle (<38) Heart Mountain detachment fault of north-western Wyoming and south-western Montana was facilitated by the presence of lubricating fluids. A recent stable isotope study suggested that the fluids along the Heart Mountain fault originated from large hydrothermal systems associated with Eocene intrusive centers. Herein, we present results from a combined stable isotope, fluid inclusion, and 40 Ar/ 39 Ar geochronology study of the relationship between shallow crustal fluids from Eocene intrusive centers in the New World Mining district and fluids associated with the Heart Mountain fault. Our results suggest that: (i) Eocene intrusive bodies within the New World Mining District focused hydrothermal fluids along specific units and structures from the ore deposit centers along the Heart Mountain fault detachment surface; (ii) hydrothermal waters were focused along the Heart Mountain fault from the breakaway region near Silvergate, Montana toward Heart Mountain in Cody, Wyoming; and (iii) hydrothermal activity along the Heart Mountain fault occurred at the same time as emplacement of the Eocene intrusives, between 50.1 and 48.1 Ma. These data, taken together, suggest that the hydrothermal activity generated by intrusion of Eocene rhyodacites and dacites provided the source of fluids found along the Heart Mountain fault plane.

Episodic Dissolution, Precipitation, and Slip along the Heart Mountain Detachment, Wyoming

“…The fault lies along the eastern margin of the extensive Absaroka volcanic field and was active during Absaroka magmatism (e.g., Hiza 2000; Douglas et al 2003;Feeley and Cosca 2003). Above the Paleozoic footwall section of the detachment, the allochthon is largely cospatial with the Sunlight volcano and is bounded to the northwest by the New World volcano ( fig.…”

“…Modified from Pierce (1980). restricts the system to processes that either function continuously or are at least repeatable thousands of times on a million-year time scale (e.g., Hauge 1982Hauge , 1985Hauge , 1990Hauge , 1993aTempleton et al 1995;Hiza 2000;Douglas et al 2003;Beutner and Hauge 2009). As such, the gradual emplacement model, if correct, starkly exposes traditional conceptions of brittle fault mechanics as having little explanatory power.…”

Quantification of mixing processes in ore-forming hydrothermal systems by combination of stable isotope and fluid inclusion analyses

“…Fluid mixing is a widely recognized process in upper crustal hydrothermal systems (e.g., Jamtveit and Hervig, 1994;Komninou and Yardley, 1997;Gleeson et al, 2000;Douglas et al, 2003;Gleeson et al, 2003;Upton et al, 2003). Mixing of fluids with different chemical composition and/or oxidation state commonly results in supersaturation of ore and gangue minerals and occurs under conditions far from equilibrium with the host rocks (e.g., Bethke, 1996).…”

10th Applied Isotope Geochemistry Conference

“…4. Douglas, T.A., Chamberlain, C.P., Poage, M.A., Abruzzese, M., Shultz, S., Henneberry, J. and Layer, P. 2003. Fluid flow and the Heart Mountain fault: A stable isotopic, fluid inclusion, and geochronologic study.…”

“…However we do not want to overlook fact that magmatic fluids assimilated one small fraction of sulfur from adjacent rocks (Ohmoto and Goldhaber, 1997). Determined range of d Buchim and Borov Dol deposits is representative for ore-bearing parts in granitic composition rocks, as it was mentioned elsewhere (Douglas et al, 2003) and porphyry Cu ± Mo deposits. Bearing in mind that the majority of sulfur isotope ratios for the Buchim and Borov Dol ranged -3.02 to +2.53‰, indicates that the source of sulfur for both deposits is clearly magmatic (Salas et al, 2013).…”