Primary Ore Minerals Research Articles

The Nabarlek uranium deposit, Northern Territory, Australia; some petrologic and geochemical constraints on genesis

The Nabarlek uranium deposit, Northern Territory, Australia, is confined to a shear zone in contorted and metasomatized early Proterozoic schists and occurs near an unconformity with overlying middle Proterozoic sandstone. Massive chlorite + or - sericite + or - hematite rocks, breccias, and intensely altered schists are characteristic of the ore zone, and at least three generations of chlorite have been recognized and described. The primary ore mineral assemblage is dominated by uraninite intergrown with chlorite. The orebody was sericitized at or after 920 m.y. ago, resulting in the widespread replacement and breakdown of chlorite, the formation of hematite, and the solution and redeposition of uraninite. Redox reactions involving iron and uranium are evident in sericitized rocks containing hematite and residual uraninite. High U/Th ratios in the ore zone suggest that uranium was transported to the site of deposition as a uranyl complex. Although no carbonaceous material occurs in the ore zone, isotopic data on minor carbonate associated with uraninite suggest that organic material was originally associated with the mineralization and indicate that these carbonates have evolved from the interaction of hydrothermal fluids with this material. Erosion of the middle Proterozoic cover rocks in the recent past has exposed themore » deposit to the effects of weathering.« less

Source of the detrital components of uraniferous conglomerates, Quirke ore zone, Elliot Lake, Ontario, Canada

Large volumes of pyritic quartz-pebble conglomerate in the Elliot Lake district of Ontario contain at least 300,000 tonnes U3O8 recoverable at a grade of 0.1% (ref. 1), with much greater tonnages available at lower recovery grades. The Quirke zone alone contains in excess of 224,000 tonnes U3O8 at ∼0.1% (refs 2–4) and is, accordingly, one of the world's largest known uranium deposits. Situated 40 km north of the North Channel of Lake Huron, 400 km north-west of Toronto, ore conglomerates occur in the Matinenda Formation, locally the basal unit of the Huronian Supergroup, and, although their age is not well constrained, they are probably close to 2,350 Myr old.5 Uraninite, the most important primary ore mineral, occurs as poorly rounded to euhedral grains 0.05–0.2 mm across within the matrix between quartz pebbles. While its chemical and morphological characteristics have led most workers to consider that the uraninite is detrital5–7, there has hitherto been no attempt to characterize its source lithology, a matter of considerable significance as regards mineral exploration. This was the aim of the present study. We have examined the mineral and fluid inclusions observed in the quartz pebbles in the conglomerate and conclude that they were derived from a pegmatitic, potassic (alaskitic) granite. We have also demonstrated that in this source lithology, pebble-sized quartz was spatially associated with radioactive minerals, by inference, uraninite. The postulated characteristics of such a source are remarkably similar in several respects to the uraniferous alaskites of the Rossing deposit in Namibia.

The Silver Hill zinc deposit and associated deposits, central North Carolina

Silver Hill is a stratiform deposit 15 m wide, 5 m thick, and at least 550 m long in chloritic argillite in a sequence of Cambrian andesitic to rhyolitic submarine pyroclastic-flow tuffs. The orebody has sharp upper and lower contacts and grades laterally into disseminated ore; chert extends for up to 200 m on either side of the orebody. Quartz-sulfide-siderite veinlets cut the argillite above and below the orebody. The ore consists of beds of fine-grained sulfides; chert, calcite, and dolomite (metamorphosed to tremolite) that precipitated with the sulfides; and argillite. Assays average 40 percent Zn, 19 percent Pb, and 0.6 percent Cu. Primary ore minerals are pyrite, sphalerite, galena, chalcopyrite, pyrrhotite, arsenopyrite, silver, freibergite, pyrargyrite, mackinawite, cubanite, bismuthinite, bismuth, magnetite, and pentlandite(?). The effect of greenschist facies metamorphism on sulfide minerals is minor. A lens of banded sphalerite-pyrite ore precipitated from a late-stage ore solution. Arsenic, bismuth, and silver were concentrated in the residual ore solution; antimony was not. An area of intense quartz mineralization marks a conduit of ore solution onto the sea floor. Other massive sulfide and quartz stringer deposits near Silver Hill are genetically related to the Silver Hill deposit.

Geologic Aspects of Uranium Resources of Japan: ABSTRACT

Uranium minerals are widespread in Japan and are present in various geologic environments. Significant concentrations of the element, however, are limited to dissemination in Tertiary sedimentary rocks of small basins. These sedimentary rocks unconformably overlie Cretaceous to Paleogene granitic rocks. The major sources of the uranium of the deposits are believed to be intergranular material and micas of the underlying granitic rocks. The average uranium content of the major granitic bodies in Japan ranges from 1.5 to 5.7 ppm, but in the vicinity of uranium concentration, can be as high as 11 ppm or more. The uranium in the rocks probably was leached by circulating groundwater containing HCO3- ion. Waters within granitic masses contain up to 8.5 ppb uranium whereas the content in average groundwater is less than 0.05 ppb. The element was transported as uranyl bicarbonate complex and deposited under reducing conditions or was adsorbed in clays and other material. The primary ore minerals of the Tono mine are uraninite and coffinite, but the major form of uranium concentration here seems to be adsorption in montmorillonite and other materials. Recently, interesting and unique deposits of the element, such as a very close association with zeolite and concentration in traps between reverse faults and the basement granite, were found in this mine. End_of_Article - Last_Page 1443------------

Sulfur isotope distribution in sulfides and sulfates from Broken Hill South, New South Wales

Sphalerite and galena are the dominant primary ore minerals found in the Broken Hill orebody of western New South Wales and both occur in minor amounts as supergene suifides, especially at Broken Hill South. Isotope values for the primary sulfides sigma S34 range from 0 to +1.7. Secondary sulfates of the same metals (anglesite and goslarite) follow these figures very closely. The sphalerite and galena of supergene origin are among the highest sigma S34 values yet recorded averaging -43.3 and reaching --51.9. This is considered due to near optimum conditions of freedom of circulation of the downward moving ground waters and thus to maximum availability of the two sulfur isotopes.

The lead-arsenic-sulfide ore deposit of Bacu Locci (Sardinia, Italy)

Arsenopyrite and galena, the principal primary ore minerals of the Bacu Locci mine area, Sardinia (Italy), occur in northwest-striking, steeply southwest-dipping fissure veins in Silurian shales and sericite gneisses, in concordant lodes within the shales, and in stockworks in younger Paleozoic lamprophyres emplaced near the end of Hercynian magmatic activity, prior to the pneumatolytic and hydrothermal processes responsible for mineralization.

Mineralogy and paragensis of the uranium ore, Mi Vida Mine, San Juan County, Utah

Ore at the Mi Vida mine, San Juan County, Utah, consists of uraninite, coffinite, montroseite, a new vanadium oxide mineral, 2 corvusite, and minor secondary minerals. The ore occurs within the matrix of the lower Chinle calcareous sandstones and conglomerates, which are colored dark gray to black by ore minerals and carbonaceous material. The primary ore minerals fill interstices in the sandstone and replace calcite and fossil wood. The replacement process was partly selective: much uraninite replaced carbonaceous debris, calcite, and detrital grains, and the vanadium minerals principally replaced calcite of the sandstone matrix. A few sulfides, pyrite, galena, and greenockite, appeared at the same time or slightly later than the primary ore. Replacement textures are common in the ore, but age relations are not clear in all cases.

Uranium ore controls of the Happy Jack deposit, White Canyon, San Juan County Utah

The major uranium ore control of the Happy Jack uranium deposit of White Canyon, San Juan County, Utah, is a paleostream channel containing sediments of the Shinarump conglomerate. Intrachannel controls include organic matter, lithologic variations, and channel lows.Microscopic studies reveal that uraninite, the primary ore mineral, occurs as cement and as a replacement of organic material. Both uraninite and copper sulfides replace secondary quartz overgrowths. Uraninite is dated as later than the secondary overgrowths and of about the same age as the copper sulfides.

Structural and stratigraphic control of zinc deposits in East Tennessee

The East Tennessee zinc district is situated in the valley regions of the Appalachians. The outstanding structural features of the valley are folds and overthrust faults which have distributed the formations into a series of belts parallel with the long axis of the valley. The same formations, duplicated by thrust faulting, outcrop in each belt. All exposed formations are sedimentary, and most of the zinc occurrences are in the Knox dolomite or the Maynardville limestone. The ore mineral is sphalerite\---|lead free, and no other sulphides except minor amounts of pyrite. At present, all producing mines are in the upper 800 to 1,100 feet of the Knox dolomite, and are situated in Knox and Jefferson Counties. Five mines and two mills are in operation. The 4,000-ton Mascot mill of the American Zinc Company is supplied by ore from the Mascot, Grasselli, Athletic and Jarnigan mines. The 900-ton mill of the Universal Exploration Company is supplied by ore from its Davis mine near Jefferson City. Sphalerite is the sole primary ore mineral, and average tenors of crude ore vary from 2.5 per cent Zn to more than 5.00 per cent Zn.The orebodies are of the replacement and breccia filling type and occur in disturbed breccia zones, which are approximately parallel to the bedding. In detail, however, this long axis may be inclined to the bedding strike. The principal structural features of the ore deposits are jointing, tear faulting, low angle thrust faulting, and bedding plane movement. Associated dolomitization is conspicuous. A major overthrust fault bounds the area in semi-circle. Within this compressive area tear fault zones are the vital structural features controlling the ore.