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Abstract
10-2 Rasmussen, Jan C., 2012, Geology, mines, and minerals of the Tombstone area (extended abstract): Minerals of Arizona, Twentieth Annual Symposium, Flagg Mineral Foundation Symposium, April 14, 2012, p. 1-5.
Abstract
10-2 Rasmussen, Jan C., 2012, Geology, mines, and minerals of the Tombstone area (extended abstract): Minerals of Arizona, Twentieth Annual Symposium, Flagg Mineral Foundation Symposium, April 14, 2012, p. 1-5.
ABS
Numerous episodes of mountain building and sedimentation have left a record in the rocks of the Tombstone Hills. The oldest rocks there are the phyllites and metarhyolites of the Pinal Schist, which was dated at 1,695 Main the nearby Little Dragoon Mountains (Silver, 1967). It is intruded by granite, which may be similar to the granite dated at 1,420 Main the nearby Little Dragoon Mountains (Silver, 1978).
The Precambrian rocks are unconformably overlain in the Tombstone Hills by a thick sequence of Paleozoic quartzite, limestone, and siltstone ranging in age from Cambrian (about 500 Ma) through Permian (about 250 Ma). These sedimentary rocks generally are excellent hosts to mineralization, as the limestones are reactive and the more resistant quartzites fracture easily under tectonic stress and provide pathways for veins and mineralization.
The Larrunide orogeny (85-43 Ma) is represented in the Tombstone Hills by three structural and two igneous-mineralization types. The east-west faulting that uplifted Government Butte was emplaced early in the Laramide and may be related to early movement on the Prompter fault. The silver mineralization in the main district was emplaced in association with northeast structures and caldera volcanism and intrusive rocks (74 Ma). A later intrusion of quartz monzonite porphyry and rhyolite (63 Ma) in the northern and eastern Tombstone Hills is of the same age and style as porphyry copper mineralization elsewhere in southern Arizona (Wilt, 1993). The principal past production from the Tombstone mining district has been silver (Ag) from high grade veins associated with the intersection of north-northeast-striking fissures and andesite dikes with the fractured crests of northwest-trending anticlines (Butler and others, 1938). Silver mineralization has been dated at 74.5 million years ago (Ma) and alteration at 72 Ma (Newell, 1974). 1t is probably related to the intrusion of the Schieffelin Granodiorite and associated tuff, the Uncle Sam Tuff, which have been dated at 76 Ma and 73.5 Ma (Creasey and Kistler, 1962; Marvin and others, 1973).
Key words
Tombstone, Cochise County, Arizona, silver, Laramide, Schieffelin Granodiorite, Uncle Sam Tuff, Tombstone mining district
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Abstract
10-2 Rasmussen, Jan C., 2012, Geology, mines, and minerals of the Tombstone area (extended abstract): Minerals of Arizona, Twentieth Annual Symposium, Flagg Mineral Foundation Symposium, April 14, 2012, p. 1-5.
ABS
Numerous episodes of mountain building and sedimentation have left a record in the rocks of the Tombstone Hills. The oldest rocks there are the phyllites and metarhyolites of the Pinal Schist, which was dated at 1,695 Main the nearby Little Dragoon Mountains (Silver, 1967). It is intruded by granite, which may be similar to the granite dated at 1,420 Main the nearby Little Dragoon Mountains (Silver, 1978).
The Precambrian rocks are unconformably overlain in the Tombstone Hills by a thick sequence of Paleozoic quartzite, limestone, and siltstone ranging in age from Cambrian (about 500 Ma) through Permian (about 250 Ma). These sedimentary rocks generally are excellent hosts to mineralization, as the limestones are reactive and the more resistant quartzites fracture easily under tectonic stress and provide pathways for veins and mineralization.
The Larrunide orogeny (85-43 Ma) is represented in the Tombstone Hills by three structural and two igneous-mineralization types. The east-west faulting that uplifted Government Butte was emplaced early in the Laramide and may be related to early movement on the Prompter fault. The silver mineralization in the main district was emplaced in association with northeast structures and caldera volcanism and intrusive rocks (74 Ma). A later intrusion of quartz monzonite porphyry and rhyolite (63 Ma) in the northern and eastern Tombstone Hills is of the same age and style as porphyry copper mineralization elsewhere in southern Arizona (Wilt, 1993). The principal past production from the Tombstone mining district has been silver (Ag) from high grade veins associated with the intersection of north-northeast-striking fissures and andesite dikes with the fractured crests of northwest-trending anticlines (Butler and others, 1938). Silver mineralization has been dated at 74.5 million years ago (Ma) and alteration at 72 Ma (Newell, 1974). 1t is probably related to the intrusion of the Schieffelin Granodiorite and associated tuff, the Uncle Sam Tuff, which have been dated at 76 Ma and 73.5 Ma (Creasey and Kistler, 1962; Marvin and others, 1973).
Key words
Tombstone, Cochise County, Arizona, silver, Laramide, Schieffelin Granodiorite, Uncle Sam Tuff, Tombstone mining district
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