Potassium-argon ages of intrusion, extrusion, and associated ore deposits, Park City mining district, Utah

Bromfield, C.S.; Erickson, A. J.; Haddadin, M. A.; Mehnert, Harald H.

doi:10.2113/gsecongeo.72.5.837

Cited by 10 publications

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“…For the Clayton Peak stock, see Palmer (1974) and Atkin (1982). For the eastern stocks, see Scales (1972); Bromfield et al (1977);and John (1989a). For the Keetley volcanic rocks, see Woodfill (1972); Leveinen (1994);and Feher (1997).…”

Section: Mineralogy Of the Stocksmentioning

confidence: 99%

“…In addition, Vogel et al (1998) presented new U-Pb, 40Ar/ 3gAr, and fission-track data, and summarized the 40Ar/3gAr, K-Ar, and fission-track data from the literature (Crittenden et al, 1973;Bromfield et al, 1977;Naeser et al, 1983;John et al, 1998). In light of the discussion by Vogel et al (1998), we consider the zircon U-Pb method to yield the best estimates of emplacement ages because of the high closing temperature involved ( > 700 OC; Hodges, 1991).…”

Section: Age Relationsmentioning

confidence: 99%

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Origin and emplacement of igneous rocks in the central Wasatch Mountains, Utah

Vogel

Cambray

Constenius

2001

Rocky Mountain Geology

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The calc-alkaline igneous rocks in the central Wasatch Mountains were emplaced between 36-30 Ma. They form a belt comprised of eleven stocks and the Keetley volcanic field aligned along the crustal suture between the Archean Wyoming province and accreted Paleoproterozoic terranes. Magmatism associated with this belt and its westward continuation into the Bingham mining district has been related to midCenozoic extension. These rocks consist of two types of stocks based on texture: a western type, which is coarse grained, and mostly equigranular, and an eastern type (including the Keetley volcanic rocks), which is fine grained and porphyritic. The compositional variation in the western stocks (Little Cottonwood, Alta, and Clayton Peak stocks) forms three distinct compositional groups. The compositional variation in the eastern stocks is similar to the compositional variation in the Alta stock. Major and trace element variations in these rocks resemble those of subduction-related magmas. However, the high KzO contents and low values are not consistent with this origin. These magmas formed from melting of mafic igneous rocks. We propose that magmas were generated by decompression melting due to gravitational collapse of the crust that had been thickened during Cretaceous to early Cenozoic deformation. Magmas rose to varying levels in the crust along a n east-west lineament. The igneous rocks of the central Wasatch Mountains have E~~(~~ similar to most of the Phanerozoic igneous rocks in the miogeocline (MG), but have significantly lower E ,~(~) .That anomaly has been explained as due to melting of a basement long depleted in Rb (Farmer andDePaolo, 1983, 1984). However, the Wasatch igneous belt rocks are high-potassium, calc-alkaline rocks and all have very similar incompatible trace element patterns, whereas only a few MG rocks are calc-alkaline or high potassium. Furthermore, in the MG rocks incompatible trace element patterns are variable. One possible explanation for the dilemma of long-time depletion of Rb in these high-potassium, calc-alkaline rocks is that the crust may have been recently charged with Rb and K during the Sevier-Laramide event (100-40 Ma) by dehydration of the subducting slab. This event was followed by melting during mid-Cenozoic collapse of the orogen (ca. 40-20 Ma). The source of the magmas was melting of mafic rocks in the lower crust. Some of these magmas ponded, formed magma chambers, and differentiated. Some involved little ponding and erupted directly on the surface in the form of the Keetley volcanic field. Continued melting and extension produced new magmas from a similar crustal source. These magmas were emplaced below a series of pull-apart structures associated with strike-slip displacement along an east-west suture. This suture may have been controlled by the ArcheanProterozoic boundary. Some magma bodies were emplaced quickly to the surface without significant fractionation. Others coalesced and fractionated over a protracted period of time. These magma bodies interacted with crus...

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Section: Mineralogy Of the Stocksmentioning

confidence: 99%

Section: Age Relationsmentioning

confidence: 99%

Origin and emplacement of igneous rocks in the central Wasatch Mountains, Utah

Vogel

Cambray

Constenius

2001

Rocky Mountain Geology

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“…2). (Crittenden et al, 1973;Bromfield et al, 1977; B. D. Turrin and D. A. They are intruded by a subvolcanic porphyry system in the Park Premier mine area and by a volcanic neck in Indian Hollow (Fig.…”

mentioning

confidence: 99%

“…They are intruded by a subvolcanic porphyry system in the Park Premier mine area and by a volcanic neck in Indian Hollow (Fig. Potassium-argon dating of hydrothermal minerals in the Park City district suggest that hydrothermal alteration and mineralization are broadly contemporaneous with intrusion of the porphyry stocks in the district and extrusion of the Keetley Volcanics (Bromfield et al, 1977). Potassium-argon dating of igneous biotite and hornblende indicate that the igneous rocks crystallized during Eocene to Oligocene time, about 43 to 31 m.y.…”

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confidence: 99%

“…Modal compositions range from diorite to monzogranite (using the IUGS classification; Streckeisen, 1976), although the bulk of the exposed rocks are granodiorites. Mineralization in the Mayflower mine may be related to the younger Ontario stock, which has the same age as hydrothermal biotite in the Mayflower mine (Bromfield et al, 1977). Small Fe-Cu skarns and Ag-Pb-Zn replacement bodies in Paleozoic carbonate rocks are associated with the Alta and Clayton Peak stocks, which exhibit only minimal hydrothermal alteration.…”

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confidence: 99%

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Geologic setting, depths of emplacement, and regional distribution of fluid inclusions in intrusions of the central Wasatch Mountains, Utah

John¹

1989

Economic Geology

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Nine mid-Tertiary calc-alkaline stocks, a subvolcanic porphyry system, and coeval volcanic rocks are exposed in a 45-km-long east-trending belt across the central Wasatch Mountains, Utah. The intrusions vary systematically from west to east in texture, style of emplacement, extent of contact metamorphism, hydrothermal alteration, and mineralization. Pressure-depth estimates based on metamorphic mineral assemblages, stratigraphic reconstructions, and fluid inclusion data indicate a regular variation in palcodepths ranging from about 11 km on the west to less than 1 km on the east. These data indicate that the central Wasatch Mountains have been tilted down to the east about 20 ø during the late Cenozoic. Fluid inclusion populations in igneous quartz also vary systematically with palcodepth; high-salinity (halite-saturated) fluid inclusions are present in the eastern porphyry stocks and in the upper parts of the Alta and Clayton Peak stocks in the center of the belt but are absent in the deeper parts of the Alta and Clayton Peak stocks and in the Little Cottonwood stock on the west side of the belt. In the Alta and Clayton Peak stocks, nearly planar high-paleosalinity horizons, presently dipping 15 ø to 20 ø east, separate rocks containing high-salinity fluid inclusions (above the high-paleosalinity horizon) from those lacking such fluid inclusions. Comparison of fluidinclusion populations in igneous and vein quartz in the Alta and Clayton Peak stocks indicates that high-salinity fluids predated most of the vein-forming hydrothermal activity and provide the earliest record of fluids to circulate in these stocks. High-salinity fluids probably formed either by boiling of fluids released during the late stages of crystallization in the parts of the intrusions where pressure was less than about 1,300 bars or by exsolution ofimmiscible highsalinity brines from the crystallizing magmas. Most hydrothermal mineralization associated with the intrusions, including Ag-Pb-Zn ores in the Park City district, are associated spatially with parts of the intrusions where high-salinity fluids were present. The major exception is the porphyry molybdenum system in the eastern part of the Little Cottonwood stock, which probably was at too great a depth (approximately 7 km) to form high-salinity brines and is dominated by low-salinity CO•-rich fluids. Introduction IN THE central Wasatch Mountains, Utah, a mid-Tertiary series of nine eale-alkaline granitoid stocks, a subvolcanic porphyry system, and coeval volcanic rocks are exposed in an east-trending belt that is the westward extension of the Uinta arch (Figs. 1 and 2). Important Ag-Pb-Zn replacement and fissure ores in the Park City district are spatially and temporally related to porphyry stocks (Barnes and Simos, 1968; Bromfield et al., 1977), and scattered base and precious metal mineralization is associated with several other stocks (Calkins and Butler, 1943; James, 1978; Bromfield and Patten, 1981). Variations in texture, style of emplaeement, hydrothermal alteration, and minerali...

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Exhumation of the central Wasatch Mountains, Utah: 1. Patterns and timing of exhumation deduced from low‐temperature thermochronology data

et al. 2003

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[1] The Wasatch Mountains are often cited as an example of normal fault growth and footwall flexure. They represent a tilted footwall at the edge of the Basin and Range extensional province, a major rift basin. Thus understanding the detailed spatial and elevation changes in coupled thermochronometer data, and how these changes can be interpreted, may aid in the analysis of thermochronometer data from other extensional regions around the world. We present a dense data set from the Cottonwood Intrusive Belt (CIB) of the Wasatch that includes apatite fission track (AFT), zircon fission track (ZFT), and apatite (U-Th)/He ages. ZFT, AFT, and apatite (U-Th)/He ages are 10, 5, and 3 Ma, respectively, adjacent to the Wasatch fault. AFT and (U-Th)/He ages increase slightly with distance east of the fault until about 15-20 km, where a more abrupt increase in these ages occurs at or near the Silver Fork-Superior fault zone. ZFT and AFT ages are concordant with 31-38 Ma pluton emplacement ages on the eastern side of range. Modeling of the data leads to the following interpretation: (1) Early cooling and $3-4 km of exhumation for the middle and eastern parts of the range occurred in the late Oligocene-middle Miocene. (2) Beginning at 10-12 Ma, the locus of exhumation shifted westward toward the present range front, where the rocks cooled from >200°C in the last 10-12 Myr. Our data and interpretations are consistent with a model in which the locus of faulting and exhumation shifted opposite the direction of tilt, similar to that predicted by rolling-hinge extensional models. However, this westward shift and rapid Miocene to recent exhumation may be a local effect superimposed on lower fault displacement and exhumation rates elsewhere along the Wasatch.

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Potassium-argon ages of intrusion, extrusion, and associated ore deposits, Park City mining district, Utah

Cited by 10 publications

References 0 publications

Origin and emplacement of igneous rocks in the central Wasatch Mountains, Utah

Origin and emplacement of igneous rocks in the central Wasatch Mountains, Utah

Geologic setting, depths of emplacement, and regional distribution of fluid inclusions in intrusions of the central Wasatch Mountains, Utah

Exhumation of the central Wasatch Mountains, Utah: 1. Patterns and timing of exhumation deduced from low‐temperature thermochronology data

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