Rocks Of Devonian Age Research Articles

Ag-Sb Deposits of the Yustid Depression, Eastern Russia and Northwest Mongolia

Ag-Sb deposits of a new economic district that occurs on the boundary of the southeastern Altay Republic of eastern Russia and northeast Mongolia are herein described. Mineralization of this region is divided into two periods—(1) Late Hercynian (Mo-W deposits) and (2) Mesozoic (Sn-W, as well as Ni-Co-As, Ag-Sb, and Sb-Hg deposits). The deposits of main economic interest, silver-antimony, consist of siderite-sulfosalt veins and vein zones that occur in contact-metamorphosed coal-bearing terrigenous rocks of Devonian age. These veins occur to depths of up to 900 m, and occur along strike for 3 to 3.5 km; their thicknesses range up to 12 m. The deposits are mineralogically and geochemically similar to silver deposits of the Yakutian, Pamir, Slovakian, Coeur D'Alene (USA), and Freiberg (Germany) ore districts. The main ore minerals are quartz, carbonate, and Ag-tetrahedrite, with minor chalcostibnite, chalcopyrite, bournonite, zinkenite, arsenopyrite, and pyrite. Sulfides are characterized by widespread isomorphism of bismuth and antimony. The deposits are characterized by a metal suite of Ag, Sb, Bi, Cu, Pb, Zn, As, and Hg, with the Ag content in the ores ranging from 250 to 600 g/t. Fluid inclusion studies demonstrate that the siderite-sulfosalt veins formed over a temperature interval of 200 to 70°C and pressures of 500 to 120 bar from highly concentrated NaCl-CaCl2-FeCl2 solutions, with CO2, CN4, and N2 dominating the gas phase. A vertical gradient of 9°C/100 m characterized the beginning of ore formation. Investigations of O, S, Pb, and Sr isotope compositions show that ore-bearing fluids were related to the final stages of crystallization of a deep magmatic center, with subsequent crystallization of Sn-W, Cu-Co-W, Ni-Co-As, and Ag-Sb ores.

The potential source of lead in the Permian Kupferschiefer bed of Europe and some selected Paleozoic mineral deposits in the Federal Republic of Germany

New lead isotopic compositions have been measured for Paleozoic bedded and vein ore deposits of Europe by the high precision thermal emission (triple filament) technique. Eleven samples have been analyzed from the Upper Permian Kupferschiefer bed with representatives from Poland to England, three samples from the Middle Devonian Rammelsberg deposit and one from the Middle Devonian Meggen deposit, both of which are conformable ore lenses and are in the Federal Republic of Germany (FRG); and also two vein deposits from the FRG were analyzed, from Ramsbeck in Devonian host rocks and from Grund in Carboniferous host rocks. For Kupferschiefer bed samples from Germany, the mineralization is of variable lead isotopic composition and appears to have been derived about 250 m.y. ago from 1700 m.y. old sources, or detritus of this age, in Paleozoic sedimentary rocks. Samples from England, Holland, and Poland have different isotopic characteristics from the German samples, indicative of significantly different source material (perhaps older). The isotopic variability of the samples from the Kupferschiefer bed in Germany probably favors the lead containing waters coming from shoreward (where poor mixing is to be expected) rather than basinward (where better mixing is likely) directions. The data thus support the interpretation of the metal source already given by Wedepohl in 1964. Data on samples from Rammelsberg and Meggen tend to be slightly less radiogenic than for the Kupferschiefer, about the amount expected if the leads were all derived from the same source material but 100 to 150 m.y. apart in time. The vein galena from Ramsbeck is similar to that from Rammelsberg conformable ore lenses, both in rocks of Devonian age; vein galena from Grund in Upper Carboniferous country rocks is similar to some bedded Kupferschiefer mineralization in Permian rocks, as if the lead composition was formed at about the same time and from similar source material as the bedded deposits. Although heat has played a more significant role in the formation of some of these deposits (veins and Rammelsberg-Meggen) than in others (Kupferschiefer), there is no indication of radically different sources for the lead, all apparently coming from sedimentary source material containing Precambrian detritus. One feldspar lead sample from the Brocken-Oker Granite is not the same in isotopic composition as any of the ores analyzed.

Developments in Illinois in 1962

In Illinois 1,839 new tests were reported drilled for oil and gas in 1962, including new oil wells in waterflood areas. In addition, 77 former dry holes were reworked and recompleted as producers, and 34 former producers were reworked and recompleted as producers in new pay zones. There were 8 oil and gas structure tests. Service well completions, mostly in waterfloods, totalled 621, including 244 new wells and 377 conversions. A total of 170 wells was completed in connection with the underground storage of natural gas. Exploratory drilling decreased 12%, from 516 wells in 1961 to 454 in 1962. Twelve new pools, 41 extensions, and 25 new pays in pools were discovered in 1962. Total oil production increased 1.41%--from 77,478,000 bbls. in 1961 to an estimated 78,543,000 bbls. in 1962. Of the 12 new pools discovered in 1962, 4 oil and 2 gas pools were discovered in Mississippian strata from Hardinsburg through Carper, 4 oil pools in rocks of Devonian age, and 2 in Silurian strata.

Rocks of Mississippian and Probable Devonian Age in Sangre de Cristo Mountains, New Mexico

In the Sangre de Cristo Mountains of northern New Mexico, Precambrian rocks are overlain by a thin but complex sequence of sandstone and limestone of pre-Pennsylvanian age. These rocks, formerly classed variously as the lower limestone member of the Sandia formation, and the Arroyo Penasco formation, are here divided into two new formations on lithologic bases. The lower formation, consisting of sandstone, sandy dolomitic limestone, and crystalline and clastic limestone, is here named the Espiritu Santo formation. The Espiritu Santo formation ranges in thickness from a trace to more than 80 feet, with an irregular but general increase in thickness from south to north. No fossils of undoubted stratigraphic significance have been found in this formation. On the basis of stratigraphic position and lithologic similarity to rocks of Devonian age in Colorado, the Espiritu Santo formation is classified as Devonian (?). Overlying the Espiritu Santo formation, with widespread erosional unconformity, is a sequence of limestone breccia and conglomerate, crystalline limestone, and calcarenite here named the Tererro formation. The Tererro formation has been divided into three members. In ascending order these are the Macho, Manuelitas, and Cowles members. The Macho member is composed of limestone breccia derived in large part from solution and collapse of cavernous parts of the upper part of the Espiritu Santo formation, and in minor part from collapsed parts of the overlying Manuelitas member. The Manuelitas member rests unconformably on the Macho member and is composed of crystalline limestone, limestone pebble and cobble conglomerate, and calcarenite. At many places these beds were involved in collapse into large sinkholes in the Macho member and Espiritu Santo formation during deposition of the Manuelitas member. The Cowles member rests unconformably on the Manuelitas member and is composed of a lower unit of calcarenite and an upper unit, present locally, of marly quartz siltstone and intercalated limestone beds. The Tererro formation ranges in thickness from a trace to 130 feet in the southern part of the Sangre de Cristo Mountains and from 6 to 48 feet thick farther north. A sparse faunule found in the Manuelitas member indicates Early Mississippian age for that part of the Tererro formation. The Tererro formation is overlain with erosional unconformity by sandstone and coaly shale beds of the Sandia formation, as here restricted, of Early Pennsylvanian age.

Stratigraphy and Structure of Moose Mountain Area, Alberta

The Moose Mountain area, situated along the front range of the Canadian Rockies, 32 miles northwest of the Turner Valley oil field, Alberta, is characterized by a large domal structure that is approximately 10 miles long and 3 miles wide, and across which is exposed a series of beds that range in age from Cretaceous to Lower Carboniferous. This structural feature has been drilled at three separated locations, resulting in two very small wells and a failure. The tests were started only a few hundred feet above the Mississippian-Devonian contact. The dry hole, drilled by the McColl-Frontenac Oil Company, was carried about 2,700 feet below the top of the Cambrian; the other wells are deriving gas and oil from rocks of Devonian age. There are bituminous limestone zones in the lower part of the Devonian that are extremely porous where they crop out north and south of the Moose Mountain area; but in the McColl-Frontenac test, where these bituminous beds were encountered structurally high, the pore spaces and fractures were filled with secondary calcite.

A "red beds" type copper occurrence, Wyoming County, Pennsylvania

Two small exposures of copper minerals in Catskill rocks of Devonian age in Wyoming Co., Pa., show mineralization of gray sandstones and shales intercalated with red strata. One prospect contains compressed and mineralized plant remnants that are semi-bituminous or anthracite in rank. Epigenetic minerals are bornite, blue and white chalcocite, and chalcopyrite. Cracks in the altered plant remnants are filled by bornite. Good preservation of cell structures probably is due to replacement of cell interiors by bornite and chalcocite. The evidence indicates that the mineralization occurred subsequent to metamorphism, and therefore it could not have occurred immediately after or accompanying the burial of the plants.

Cave-sandstone deposits of the southern Ozarks

Stratigraphy of the southern Ozarks The surface rocks of the southern Ozarks are of Ordovician, Silurian, Devonian, and Carboniferous ages. Those of Silurian age are absent over a large portion of the region, as a result of unconformities, and those of Carboniferous age are locally absent, as a result of erosion during the present erosion cycle. In southern Missouri and northern Arkansas the streams have in many places cut far below the Carboniferous rocks, leaving the older rocks exposed on the hillsides. The rocks of Devonian age consist of a thin stratum of sandstone, or of sandstone and shale, and as those of Silurian age are usually absent, practically all the rocks exposed below those of Carboniferous age belong to the Ordovician. Near the Arkansas-Missouri line the Ordovician rocks exposed along the sides of the rather deep ravines consist of manganesian limestone containing several beds that are more or less . . .