Stratabound Base-metal Deposits Research Articles

Multiple episodes of fluid flow in base-metal deposits from southwest Scotland and Northern Ireland

Cathodoluminesence zones allow correlation of mineralizing and brecciation events in sulphide-bearing quartz veins from strata-bound base-metal deposits in the Southern Uplands of southwest Scotland and Northern Ireland. Ore-bearing veins are typically associated with NNW–SSE to NW–SE and E–W to NE–SW trending fractures and brittle fault zones. Two main ages of stratabound base-metal mineralization have occurred in this region; a late Caledonian, high temperature phase and a younger low temperature, lower Carboniferous phase. Between three and six cathodoluminescence zones were identified in a number of deposits. The similarity in cathodoluminescence zones developed at different deposits reflects similar broad fluctuations in the chemistry of ore-bearing fluids, correlated over a region of 120km. Multiple episodes of brecciation during quartz and sulphide deposition suggests that faulting was an active process during hydrothermal activity. Quartz from Caledonian mineralization contains cathodoluminescence zones, which are texturally distinct in comparison with the quartz from subsequent lower Carboniferous mineralization.

TOURMAL: software package for tourmaline, tourmaline-rich rocks and related ore deposits

TOURMAL is a user-friendly software package developed for editing, storing, calculating and plotting microprobe tourmaline analyses from different geologic environments such as granites and their related aplites and pegmatites, metasomatic and vein type ore deposits, stratabound base metal deposits, gold deposits, and sedimentary and metamorphic rocks. Calculated results, saved in comma delimited ASCII file format, permit the user to search for other applications related to tourmaline compositions. The program prepares 28 binary and seven ternary diagrams. It is written in Quickbasic for IBM PC and compatibles, and runs under DOS and Windows operating systems with a VGA graphic card. This program permits the user to convert standard binary graphs and ternary diagrams into PCX file format for high quality printouts.

A Framework for North Slope Seminar II: ABSTRACT

This meeting focuses on a province with enormous potential for fuels and minerals. Oil reserves approach 10% of the total oil already produced in the rest of the country. Estimated coal resources could store a thousand times the 70-80 quads of energy the U.S. uses every year. Potential yields of silver, lead, and zinc range from 10 to 100% of the amounts produced domestically since the middle of the 19th century. Prospects for copper are also large. The province is dominated by the east-trending Brooks Range, whose structures formed during the late Mesozoic Brookian orogeny and are now being shortened longitudinally. Flanking basins succeeded the uplift; the northern one is bounded by a passive continental margin. Early in the orogeny, a relatively thin early Paleozoic through Jurassic megasequence of clastic-wedge, carbonate, and siliceous sediments was telescoped into a fivefold stacking of allochthons and beneath allochthons of volcanic and mafic-ultramafic rocks. The greater than 500-km breadth of sialic crust that had underlain the allochthons disappeared. At about the same time, the Arctic Ocean basin replaced the northern provenance. A mid-Paleozoic sialic source area on the opposite margin of the megasequence disappeared y the end of the Carboniferous and near the beginning of siliceous deposition. Basement beneath the North Slope part of the mega-sequence was created when the Devonian Ellesmerian orogeny added to the crust the late Precambrian to early Paleozoic clastic, carbonate, and volcanic rocks of an older megasequence. The northern successor basin accumulated large amounts of coal. Truncation and sealing of potential reservoir rocks on replacement of the northern landmass led to huge pools of hydrocarbons. Late Paleozoic rocks in the lowest allochthon host stratabound base-metal deposits. A narrow belt of reportedly Devonian shallow-seated felsic rocks contain deposits of copper. John Maher foresaw the benefits that the first North Slope seminar has provided. That precedent and developments during the past 15 years promise similar benefits from this meeting. End_of_Article - Last_Page 680------------

A discussion of the paper by E. F. Stumpfl ?Manganese haloes surrounding metamorphic stratabound base metal deposits?

A discussion of the paper by E. F. Stumpfl ?Manganese haloes surrounding metamorphic stratabound base metal deposits?

A discussion of the paper by E. F. Stumpfl ?Manganese haloes surrounding metamorphic stratabound base metal deposits?

A discussion of the paper by E. F. Stumpfl ?Manganese haloes surrounding metamorphic stratabound base metal deposits?

Manganese haloes surrounding metamorphic stratabound base metal deposits

Primary manganese haloes "survive" medium to high-grade regional metamorphism: stratabound base metal deposits in Namaqualand, N. W. Cape Province (Proterozoic) and in the Eastern Alps (Paleozoic and Mesozoic) reveal an increase in Mn as the ore horizon (and associated BIF) is approached from the hangingwall or the footwall. Electron microprobe analyses show Mn to be preferentially concentrated in garnets; compositions vary considerably and include pure spessartine (40 % MnO). Compositional inhomogeneities (zoning) appear to be confined to garnets in lower grade metamorphic terranes. Iron contents of associated sphalerite vary within meters of the stratigraphic sequence and even within one polished section; sphalerite geobarometry does not appear promising in these environments.

Metallogenesis in the Japanese island arc system

Ore deposits in the Mesozoic and Cenozoic orogenic belts of the Japanese island arc system consist essentially of stratabound, vein and skarn types. The stratabound base-metal deposits, which are the main source of copper, are divided into the lead-free, chalcopyrite-pyrite, Besshi-type, which occur mainly in glaucophane schists (metamorphosed basaltic pyro-clastic rocks) of the Sanbagawa belt, and the lead-bearing, polymetallic, massive sulphide, Kuroko-type, associated with rhyolite extrusion. Both types are regarded as having been formed syngenetically in a submarine environment. Vein-type deposits are widely distributed and economically the most important for metals, containing more than 50 per cent of the available tin, tungsten, molybdenum, gold, silver and manganese. The ore deposits are genetically related to either 'geosynclinal basalt' or an andesite-dacite-rhyolite and plutonic association of island arc magmatism. Special attention is given to deposits of plutonic affinity. Most Japanese plutons are granitoids. Ore deposits associated with Cretaceous-Palaeogene granitoids in southwest Japan constitute two metallogenic provinces, characterised by W-Sn-Cu and Mo-Pb-Zn veins and skarns. Northeast Japan shows a similar, but reversed, zoning, with no tin. Miocene granitoids in southwest Japan are accompanied by tin and some copper mineralization. The Japanese granitoids consist of approximately equal proportions of magnetite-series and ilmenite-series rocks. The magnetite-series is thought to be derived from a parental magma generated from mafic igneous rocks of the upper mantle—lower crust and related to major subduction. The ilmenite-series, with which tin deposits may be associated, is ascribed to magma originating in the lower crust from sedimentary, metamorphic and granitoid rocks. These magma types appear to be the most important factors in producing the various metallogenic provinces in Japan.