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Vein Deposits (vein + deposit)

Distribution by Scientific Domains
Earth and Environmental Science100%

Selected Abstracts

Rare Earth Deposits of North America

RESOURCE GEOLOGY, Issue 4 2008
Stephen B. Castor
Abstract Rare earth elements (REE) have been mined in North America since 1885, when placer monazite was produced in the southeast USA. Since the 1960s, however, most North American REE have come from a carbonatite deposit at Mountain Pass, California, and most of the world's REE came from this source between 1965 and 1995. After 1998, Mountain Pass REE sales declined substantially due to competition from China and to environmental constraints. REE are presently not mined at Mountain Pass, and shipments were made from stockpiles in recent years. Chevron Mining, however, restarted extraction of selected REE at Mountain Pass in 2007. In 1987, Mountain Pass reserves were calculated at 29 Mt of ore with 8.9% rare earth oxide based on a 5% cut-off grade. Current reserves are in excess of 20 Mt at similar grade. The ore mineral is bastnasite, and the ore has high light REE/heavy REE (LREE/HREE). The carbonatite is a moderately dipping, tabular 1.4-Ga intrusive body associated with ultrapotassic alkaline plutons of similar age. The chemistry and ultrapotassic alkaline association of the Mountain Pass deposit suggest a different source than that of most other carbonatites. Elsewhere in the western USA, carbonatites have been proposed as possible REE sources. Large but low-grade LREE resources are in carbonatite in Colorado and Wyoming. Carbonatite complexes in Canada contain only minor REE resources. Other types of hard-rock REE deposits in the USA include small iron-REE deposits in Missouri and New York, and vein deposits in Idaho. Phosphorite and fluorite deposits in the USA also contain minor REE resources. The most recently discovered REE deposit in North America is the Hoidas Lake vein deposit, Saskatchewan, a small but incompletely evaluated resource. Neogene North American placer monazite resources, both marine and continental, are small or in environmentally sensitive areas, and thus unlikely to be mined. Paleoplacer deposits also contain minor resources. Possible future uranium mining of Precambrian conglomerates in the Elliott Lake,Blind River district, Canada, could yield by-product HREE and Y. REE deposits occur in peralkaline syenitic and granitic rocks in several places in North America. These deposits are typically enriched in HREE, Y, and Zr. Some also have associated Be, Nb, and Ta. The largest such deposits are at Thor Lake and Strange Lake in Canada. A eudialyte syenite deposit at Pajarito Mountain in New Mexico is also probably large, but of lower grade. Similar deposits occur at Kipawa Lake and Lackner Lake in Canada. Future uses of some REE commodities are expected to increase, and growth is likely for REE in new technologies. World reserves, however, are probably sufficient to meet international demand for most REE commodities well into the 21st century. Recent experience shows that Chinese producers are capable of large amounts of REE production, keeping prices low. Most refined REE prices are now at approximately 50% of the 1980s price levels, but there has been recent upward price movement for some REE compounds following Chinese restriction of exports. Because of its grade, size, and relatively simple metallurgy, the Mountain Pass deposit remains North America's best source of LREE. The future of REE production at Mountain Pass is mostly dependent on REE price levels and on domestic REE marketing potential. The development of new REE deposits in North America is unlikely in the near future. Undeveloped deposits with the most potential are probably large, low-grade deposits in peralkaline igneous rocks. Competition with established Chinese HREE and Y sources and a developing Australian deposit will be a factor. [source]

Fluid evolution in base-metal sulphide mineral deposits in the metamorphic basement rocks of southwest Scotland and Northern Ireland

GEOLOGICAL JOURNAL, Issue 1 2005
Martin Baron
Abstract The Dalradian and Ordovician,Silurian metamorphic basement rocks of southwest Scotland and Northern Ireland host a number of base-metal sulphide-bearing vein deposits associated with kilometre-scale fracture systems. Fluid inclusion microthermometric analysis reveals two distinct fluid types are present at more than half of these deposits. The first is an H2O,CO2,salt fluid, which was probably derived from devolatilization reactions during Caledonian metamorphism. This stage of mineralization in Dalradian rocks was associated with base-metal deposition and occurred at temperatures between 220 and 360°C and pressures of between 1.6 and 1.9,kbar. Caledonian mineralization in Ordovician,Silurian metamorphic rocks occurred at temperatures between 300 and 360°C and pressures between 0.6 and 1.9,kbar. A later, probably Carboniferous, stage of mineralization was associated with base-metal sulphide deposition and involved a low to moderate temperature (Th 70 to 240°C), low to moderate salinity (0 to 20,wt% NaCl eq.), H2O,salt fluid. The presence of both fluids at many of the deposits shows that the fractures hosting the deposits acted as long-term controls for fluid migration and the location of Caledonian metalliferous fluids as well as Carboniferous metalliferous fluids. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Compositional Variation of Hydrothermally Altered Volcanic Rocks in Hishikari Gold Epithermal System: A Useful Geochemical Indicator of Gold,Silver Epithermal Mineralization

RESOURCE GEOLOGY, Issue 2 2010
Naotatsu Shikazono
Abstract The hydrothermally altered andesite hosting the Hishikari gold-silver vein deposits in southern Kyushu, Japan, is analyzed with respect to the spatial variation in chemical composition. The (CaO + Na2O) content is found to be inversely correlated with the K2O content as it progresses away from the site of mineralization. It was found that analytical data plotted on a (CaO + Na2O) , K2O diagram cannot be explained only by addition of K+ from the hydrothermal solution to the original rock and release of Ca2+ and Na+ from the original rock (K- alteration). Addition of Ca2+ and Na+ from the hydrothermal solution to the rock and release of K+ from the rock but release of K+, Ca2+, and Na+ to the hydrothermal solution (advanced argillic alteration) is important for causing the wide variations in K2O, CaO, and Na2O contents on the (CaO + Na2O) , K2O diagram. These variations can be explained by superimposed potassic, advanced argillic and calcium alterations. The altered rocks in the Honko-Sanjin area, Yamada area, and Masaki area analyzed by this study are characterized by their intermediate K2O content and variable CaO content, high K2O content and low CaO content, and low K2O content and low CaO content, respectively. The K2O, Na2O and CaO contents and oxygen isotopic composition of altered andesite, in conjunction with the solubility of gold as a thio complex, suggest that both gold deposition and the observed compositional variation of altered andesite are the result of mixing between acidic groundwater and neutral gold-bearing hydrothermal solution. The present results indicate that the compositional variation of hydrothermally altered rocks may represent a useful geochemical indicator of epithermal gold,silver mineralization. [source]

Rare Earth Deposits of North America

RESOURCE GEOLOGY, Issue 4 2008
Stephen B. Castor
Abstract Rare earth elements (REE) have been mined in North America since 1885, when placer monazite was produced in the southeast USA. Since the 1960s, however, most North American REE have come from a carbonatite deposit at Mountain Pass, California, and most of the world's REE came from this source between 1965 and 1995. After 1998, Mountain Pass REE sales declined substantially due to competition from China and to environmental constraints. REE are presently not mined at Mountain Pass, and shipments were made from stockpiles in recent years. Chevron Mining, however, restarted extraction of selected REE at Mountain Pass in 2007. In 1987, Mountain Pass reserves were calculated at 29 Mt of ore with 8.9% rare earth oxide based on a 5% cut-off grade. Current reserves are in excess of 20 Mt at similar grade. The ore mineral is bastnasite, and the ore has high light REE/heavy REE (LREE/HREE). The carbonatite is a moderately dipping, tabular 1.4-Ga intrusive body associated with ultrapotassic alkaline plutons of similar age. The chemistry and ultrapotassic alkaline association of the Mountain Pass deposit suggest a different source than that of most other carbonatites. Elsewhere in the western USA, carbonatites have been proposed as possible REE sources. Large but low-grade LREE resources are in carbonatite in Colorado and Wyoming. Carbonatite complexes in Canada contain only minor REE resources. Other types of hard-rock REE deposits in the USA include small iron-REE deposits in Missouri and New York, and vein deposits in Idaho. Phosphorite and fluorite deposits in the USA also contain minor REE resources. The most recently discovered REE deposit in North America is the Hoidas Lake vein deposit, Saskatchewan, a small but incompletely evaluated resource. Neogene North American placer monazite resources, both marine and continental, are small or in environmentally sensitive areas, and thus unlikely to be mined. Paleoplacer deposits also contain minor resources. Possible future uranium mining of Precambrian conglomerates in the Elliott Lake,Blind River district, Canada, could yield by-product HREE and Y. REE deposits occur in peralkaline syenitic and granitic rocks in several places in North America. These deposits are typically enriched in HREE, Y, and Zr. Some also have associated Be, Nb, and Ta. The largest such deposits are at Thor Lake and Strange Lake in Canada. A eudialyte syenite deposit at Pajarito Mountain in New Mexico is also probably large, but of lower grade. Similar deposits occur at Kipawa Lake and Lackner Lake in Canada. Future uses of some REE commodities are expected to increase, and growth is likely for REE in new technologies. World reserves, however, are probably sufficient to meet international demand for most REE commodities well into the 21st century. Recent experience shows that Chinese producers are capable of large amounts of REE production, keeping prices low. Most refined REE prices are now at approximately 50% of the 1980s price levels, but there has been recent upward price movement for some REE compounds following Chinese restriction of exports. Because of its grade, size, and relatively simple metallurgy, the Mountain Pass deposit remains North America's best source of LREE. The future of REE production at Mountain Pass is mostly dependent on REE price levels and on domestic REE marketing potential. The development of new REE deposits in North America is unlikely in the near future. Undeveloped deposits with the most potential are probably large, low-grade deposits in peralkaline igneous rocks. Competition with established Chinese HREE and Y sources and a developing Australian deposit will be a factor. [source]