Browsing by Subject "volcanism"

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Calderas and Mineralization Volcanic Geology and Mineralization in the Chinati Caldera Complex, Trans-Pecos Texas
(1981) Duex, Timothy W.; Henry, Christopher D.
This report describes preliminary results of an ongoing study of the volcanic stratigraphy, caldera activity, and known and potential mineralization of the Chinati Mountains area of Trans-Pecos Texas. Many ore deposits are spatially associated with calderas and other volcanic centers. A genetic relationship between calderas and base and precious metal mineralization has been proposed by some (Albers and Kleinhampl, 1970) and denied by others (McKee, 1976, 1979). Steven and others (1974) have demonstrated that calderas provide an important setting for mineralization in the San Juan volcanic field of Colorado. Mineralization is not found in all calderas but is apparently restricted to calderas that had complex, post-subsidence igneous activity. A comparison of volcanic setting, volcanic history, caldera evolution, and evidence of mineralization in Trans-Pecos to that of the San Juan volcanic field, a major mineral producer, indicates that Trans-Pecos Texas also could be an important mineralized region. The Chinati caldera complex in Trans-Pecos Texas contains at least two calderas that have had considerable post-subsidence activity and that display large areas of hydrothermal alteration and mineralization. Abundant prospects in Trans-Pecos and numerous producing mines in the continuation of the Trans-Pecos volcanic field immediately south in Mexico are additional evidence that ore-grade deposits could occur in Texas.
Letter to F.K.G. Mullerried from H.B. Stenzel on 1942-09-14
(1942-09-14) Stenzel, H.B.
Report of Investigations No. 135 Oligocene Volcanism and Multiple Caldera Formation in the Chinati Mountains, Presidio County, Texas
(University of Texas at Austin. Bureau of Economic Geology, 1983) Cepeda, Joseph C.; Henry, Christopher D.
The Chinati Mountains caldera, which lies in Trans-Pecos Texas in the southern Basin and Range Province, was formed by eruption of the Mitchell Mesa Rhyolite. The caldera (30 km by 20 km) is part of a larger Oligocene volcanic province that includes Trans-Pecos Texas and extends to the Sierra Madre Occidental of western Mexico. Volcanism in the Chinati Mountains area began several million years before formation of the Chinati Mountains caldera. Rocks of the Morita Ranch Formation, Infiernito caldera, and Shely Group ring the caldera on the south, east, and north. After its collapse, the caldera was filled by rhyolitic to trachytic lava flows and an ash-flow tuff of the Chinati Mountains Group. These include, from oldest to youngest, the lower trachyte, middle trachyte, lower rhyolite, upper trachyte, and upper rhyolite (ash-flow tuff). The Chinati Mountains Group was then intruded by the West Chinati Stock, the resurgent dome of the caldera. Three cycles of rhyolitic to trachytic magmatism, all derived from a zoned magma chamber, are represented by (1) Mitchell Mesa Rhyolite to lower and middle trachytes, (2) lower rhyolite to upper trachyte, and (3) upper rhyolite to West Chinati Stock. Dominant caldera collapse followed eruption of the Mitchell Mesa Rhyolite, but collapse is also associated with rhyolitic eruptions in the second and third cycles. The entire sequence erupted between 32 and 33 mya. The Chinati Mountains area is the site of one major, inactive silver mine and numerous prospects for silver, lead, zinc, copper, molybdenum, uranium, and fluorite. The Shafter silver district produced 31 million ounces of silver from Permian dolomitic limestones just south of the southern boundary of the caldera. Major prospects are associated with a quartz-monzonite porphyry intrusion (copper-molybdenum) just west of Shafter and with the West Chinati Stock (silver, lead, zinc, copper, and fluorite). All mineralization is probably genetically related to the caldera.
Volanic Geology of the Davis Mountains Trans-Pecos Texas: First Year Report
(1988) Henry, Christopher D.
This report describes the results of the first-year study of the volcanic rocks of the Davis Mountains, Trans-Pecos Texas. Oligocene volcanic rocks in the Davis Mountains constitute the major part of the eastern, alkalic belt of the Trans-Pecos volcanic field. Yet, because of their volcanic and stratigraphic complexity, the Davis Mountains remain the most poorly mapped and least understood part of the field. The geology of the Davis Mountains as shown on the Geologic Atlas of Texas is based on regional extrapolation of formations established in a few detailed studies. Unfortunately, even these detailed studies commonly grouped a variety of lithologic types of doubtful genetic relationship. Extrapolation of these composite units into areas studied only from aerial photographs has further confused true relations. Very few source areas, calderas or otherwise, have been even tentatively identified. Only one stratovolcano and one caldera have been relatively thoroughly studied. Nevertheless, the Davis Mountains are worthy of detailed study for several reasons. They are a distinctive, large-scale example of alkalic continental volcanism, comparable in areal extent and volume to major calcalkalic fields such as the San Juan Mountains of Colorado. All igneous rocks are alkalic; several are peralkaline. The volume of individual volcanic units is much greater than in most peralkaline volcanic fields. Many of the ash-flow sheets are rheomorphic; the degree of secondary flow ranges up to extreme examples in which a pyroclastic origin is largely obscured. Additionally, several large-volume silicic units have the outcrop and textural scale features of lavas but the areal dimensions of ash-flow tuffs. The origin of these units, whether extremely rheomorphic tuffs or unusually large-volume and extensive silicic lavas, is actively debated.
Volcanic Geology of the Davis Mountains, Trans-Pecos Texas: Second Year Report
(1989) Henry, Christopher D.
This report describes the results of the second year of mapping of the volcanic rocks of the Davis Mountains, Trans-Pecos Texas. The Davis Mountains (fig. 1) constitute a major part of the eastern, alkalic belt of the Trans-Pecos volcanic field (Barker, 1977; Price and others, 1986). Yet, because of their volcanic and stratigraphic complexity, the Davis Mountains remain the most poorly mapped and least understood part of the field. Published geologic maps of the area (the Fort Stockton and Marfa sheets of the Geologic Atlas of Texas (McKalips and others, 1982; Twiss, 1979)) are based on regional, aerial photographic extrapolation of formations established in a few detailed studies.