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Minerals & deposits

Find USGS publications on mineral resources and deposits. Search commodities and geographic names, then check source reports for geology and assessment methods.

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USGS1981

Mineral deposits and geology of northern Oman as of 1974

An investigation of the mineral resources of northern Oman was carried out under an agreement between the U. S. Geological Survey and the Ministry of Development, Sultanate of Oman, during late 1973 and early 1974. The purpose of the investigation was to provide an evaluation of the mineral potential of northern Oman and produce recommendations leading toward the utilization of any viable mineral deposits that were found. The widespread copper deposits located within the Semail volcanics appear to be mineable, the iron-nickel laterites developed upon the weathered surface of the Semail ophiolite have economic potential. Manganese and chromite deposits investigated have only a marginal value and are not likely to be of economic importance in the near future. Discovery of economic copper and iron deposits warrants further geologic mapping and mineral exploration in northern Oman. In addition to this, recommendations regarding the organization of a geological and mining group within the Directorate of Petroleum and Minerals are presented.

Open-File Report↗

USGS1982

Digital data base application to porphyry copper mineralization in Alaska; case study summary

The purpose of this report is to summarize the progress in use of digital image analysis techniques in developing a conceptual model for assessing porphyry copper mineral potential. The study area consists of approximately the southern one-half of the 1? by 3? Nabesna quadrangle in east-central Alaska. The digital geologic data base consists of data compiled under the Alaskan Mineral Resource Assessment Program (AMRAP) as well as digital elevation data and Landsat spectral reflectance data from the Multispectral Scanner System. The digital data base used to develop and implement a conceptual model for porphyry-type copper mineralization consisted of 16 original data types and 18 derived data sets formatted in a grid-cell (raster) structure and registered to a map base in the Universal Transverse Mercator (UTM) projection. Minimum curvature and inverse distance squared interpolation techniques were used to generate continuous surfaces from sets of irregularly spaced data points. Processing requirements included: (1) merging or overlaying of data sets, (2) display and color coding of maps and images, (3) univariate and multivariate statistical analyses, and (4) compound overlaying operations. Data sets were merged and processed to create stereoscopic displays of continuous surfaces. The ratio of several data sets were calculated to evaluate relative variations and to enhance the display of surface alteration (gossans). Factor analysis and principal components analysis techniques were used to determine complex relationships and correlations between data sets. The resultant model consists of 10 parameters that identify three areas most likely to contain porphyry copper mineralization; two of these areas are known occurrences of mineralization and the third is not well known. Field studies confirmed that the three areas identified by the model have significant copper potential.

Open-File Report↗

USGS1983

A preliminary evaluation of stream sediment sampling for the detection of cobalt mineralization in the Bou Azzer District, Morocco

Analyses of 28 stream sediment samples collected in the Bou Azzer district, Morocco, show that this sampling technique may be useful in locating the cobalt arsenide mineralization that exists in this area. The absence of exceptionally high values of cobalt and arsenic, the nearly lognormal distribution of cobalt values, and the lack of correlation between the highest values of cobalt and arsenic were unanticipated results that do not support the use of this sampling technique. However, highest values of several metals, including cobalt, were associated with an identified area of cobalt mineralization, and high cobalt was present near a second area in which cobalt mineralization is suspected. Although probably mostly reflecting the geochemistry of unexposed ultramafic rocks, the association of these metals with mineralization shows that this type of sampling can independently locate areas of known or potential cobalt mineralization.

Open-File Report↗

USGS1984

An evaluation of the applicability of the telluric-electric and audio-magnetotelluric methods to mineral assessment on the Arabian Shield, Kingdom of Saudi Arabia

Feasibility studies of two electromagnetic methods were made in selected areas of the Jabal Hibshi (1:250,000) quadrangle, 26F, in the Kingdom of Saudi Arabia in March of 1983. The methods tested were the natural source-field telluricelectric and audio-magnetotelluric methods developed and extensively used in recent years by the U.S. Geological Survey in some of its domestic programs related to geothermal and mineral resource assessment. Results from limited studies in the Meshaheed district, the Jabal as Silsilah ring complex, and across a portion of the Raha fault zone clearly demonstrate the appropriateness of these sub-regional scale, reconnaissance-type studies to mineral resource assessment. The favorable results obtained are largely attributed to distinctive and large contrasts in the electrical resistivity of the major rock types encountered. It appears that the predominant controlling factor governing the rock resistivities is the amount of contained clay minerals. Accordingly, unaltered (specifically, non-argillic) igneous and metamorphic rocks have very high resistivities; metasedimentary rocks of the Murdama group that contain several percent clay minerals have intermediate values of resistivity; and highly altered rocks, containing abundant clay minerals, have very low values of resistivity. Water-filled fracture porosity may be a secondary, but important, factor in some settings. However, influences from variations in interstitial or intercrystalline, water-filled porosity are probably small because these types of porosity are generally low. It is reasonable to expect similar results in other areas within the Arabian Shield.

Open-File Report↗

USGS1981

Metamorphic mineral assemblages of slightly calcic pelitic rocks in and around the Taconic Allochthon, southwestern Massachusetts and adjacent Connecticut and New York

The mineral assemblages from metamorphosed slightly calcic pelitic rocks of the Taconic Range in southwestern Massachusetts and adjacent areas of Connecticut and New York were studied petrographically and chemically. These rocks vary in metamorphic grade from those below the chloritoid zone through the chloritoid and garnet zones into the kyanite-staurolite zone. Microprobe data on the ferromagnesian minerals show that the sequence of increasing Fe/ (Fe+Mg) value is, from the lowest, chlorite, biotite, hornblende, chloritoid, staurolite, garnet. Hornblende, epidote, garnet, and plagioclase are the most common minerals that carry significant calcium. Biotite is persistently deficient in alkali but is abnormally rich in octahedral aluminum to such an extent that the overall charge balance can be ascribed to an AI=K+ (Fe,Mg) diadochy. Muscovite contains small though persistent amounts of iron and magnesium in octahedral positions but has a variable K/Na ratio, which is potentially useful as a geothermometer. One low-grade muscovite is highly phengitic, but the white micas in rocks from metamorphic grades higher than chloritoid zone do not contain significant phengite components. Chlorite is persistently high in aluminum and so its ratio of divalent ions to aluminum is approximately that of garnet. Many garnets show pronounced zoning in manganese and less pronounced zoning in calcium. Garnet coexisting with hornblende contains a high proportion of the grossularitic component. The calcium content is significant in all the analyzed garnets, except those from a cummingtonite-bearing sample that is free of muscovite. This suggests that in slightly calcic pelitic rocks, calcium-free garnet cannot coexist with muscovite. Most of the mineral assemblages formed in the presence of excess quartz and muscovite. The phase-petrologic analysis, made with the aid of an eight-phase multisystematic model, shows the following major points: 1. Chloritoid and staurolite coexist in a definite interval of prograde metamorphism. 2. Biotite-chloritoid does not constitute an alternative assemblage to garnet-chlorite-muscovite, because the former combination is found predominantly in the presence of the latter combination. Because the garnet contains lime, all five phases are stable together in lowlime pelitic rocks. 3. The first appearance of staurolite in the area does not correspond to the reaction leading to the first intrinsic stable existence of this phase. Inasmuch as the first appearanc,e of staurolite is always in chlorite-bearing as semblages, I suggest that the mapped staurolite zone marker corresponds to a reaction whereby staurolitechlorite becomes stable. The probable lower grade chemical equivalent, for example, chloritoid-aluminum silicate, however, has not been found in the area of study. Several staurolite-forming reactions discussed in the literature are ruled out because of the relative siderophility of the minerals. A second staurolite isograd involves the reaction, chloritoid+chlorite+muscovite= staurolite+biotite. A third isograd involves staurolite+ chlorite=biotite+kyanite; this reaction is postulated on the basis of the observed assemblage biotite-kyanitesta urolite-garnet-muscoviteplagioclase-quartzilmenite. 4. In low-grade rocks, epidote is stable considerably before the first appearance of chloritoid. The nature of the high-aluminum phase in low-grade rocks that leads to the formation of chloritoid remains obscure. The epidote is always rich in ferric iron (pistacite content of about 1/ 4 to 1/3). Garnet-bearing assemblages (with or without epidote) are formed next as metamorphic grade increases. The next more calcium-rich silicate is hornblende, and despite the meager data on assemblages that include hornblende, the first intrinsic appearance of this phase has probably been recorded. At highstaurolite grade, the most calcium-rich assemblage in pelitic rocks is hornblende-garnet-biotite-plagioclase (bytownit

Professional Paper↗

USGS2011

Investigation of the potential for concealed base-metal mineralization at the Drenchwater Creek Zn-Pb-Ag occurrence, northern Alaska, using geology, reconnaissance geochemistry, and airborne electromagnetic geophysics

In 2005, the U.S. Geological Survey, Bureau of Land Management, and State of Alaska cooperated on an investigation of the mineral potential of a southern part of the National Petroleum Reserve in Alaska, Howard Pass quadrangle, to provide background information for future land-use decisions. The investigation incorporated an airborne electromagnetic (EM) survey covering 1,500 mi 2 (~3,900 km 2 ), including flight lines directly over the Drenchwater Creek sediment-hosted Zn-Pb-Ag occurrence, the largest known base-metal occurrence in the survey area. Samples from the mineralized outcrop and rubblecrop contain metal concentrations that can exceed 11 percent Zn+Pb, with appreciable amounts of Ag. Soil samples with anomalous Pb concentrations are distributed near the sulfide-bearing outcrops and along a >2.5 km zone comprising mudstone, shale, and volcanic rocks of the Kuna Formation. No drilling has taken place at the Drenchwater occurrence, so alternative data sources (for example, geophysics) are especially important in assessing possible indicators of mineralization. Data from the 2005 electromagnetic survey define the geophysical character of the rocks at Drenchwater and, in combination with geological and surface-geochemical data, can aid in assessing the possible shallow (up to about 50 m), subsurface lateral extent of base-metal sulfide accumulations at Drenchwater. A distinct >3-km-long electromagnetic conductive zone (observed in apparent resistivity maps) coincides with, and extends further westward than, mineralized shale outcrops and soils anomalously high in Pb concentrations within the Kuna Formation; this conductive zone may indicate sulfide-rich rock. Models of electrical resistivity with depth, generated from inversion of electromagnetic data, which provide alongflight-line conductivity-depth profiles to between 25 and 50 m below ground surface, show that the shallow subsurface conductive zone occurs in areas of known mineralized outcrops and thins to the east. Broader, more conductive rock along the western ~1 km of the geophysical anomaly does not reach ground surface. These data suggest that the Drenchwater deposit is more extensive than previously thought. The application of inversion modeling also was applied to another smaller geochemical anomaly in the Twistem Creek area. The results are inconclusive, but they suggest that there may be a local conductive zone, possibly due to sulfides.

Professional Paper↗

USGS2016

Global stocks of selected mineral-based commodities

Introduction The U.S. Geological Survey, National Minerals Information Center, analyzes mineral and metal supply chains by identifying and describing major components of mineral and material flows from ore extraction, through intermediate forms, to a final product. This report focuses on an important component of the world’s supply chain: the amounts and global distribution of major consumer, producer, and exchange stocks of selected mineral commodities. In this report, the term “stock” is used instead of “inventory” and refers to accumulations of mined ore, intermediate products, and refined mineral-based commodities that are in a form that meets the agreed-upon specifications of a buyer or processor of intermediate products. These may include certain ores such as bauxite, concentrates, smelter products, and refined metals. Materials sometimes referred to as inventory for accounting purposes, such as ore contained in a deposit or in a leach pile, or materials that need to be further processed before they can be shipped to a consumer, are not considered. Stocks may be held (owned) by consumers, governments, investors, producers, and traders. They may serve as (1) a means to achieve economic, social, and strategic goals through government policies; (2) a secure source of supply to meet demand and to mitigate potential shortages in the supply chain; (3) a hedge to mitigate price volatility; and (4) vehicles for speculative investment. The paucity and uneven reliability of data for stocks of ores and concentrates and for material held by producers, consumers, and merchants hinder the accurate estimating of the size and distribution of this portion of the supply chain for certain commodities. This paper reviews the more visible stocks held in commodity exchange warehouses distributed throughout the world.

Scientific Investigations Report↗

USGS2023

Creating oriented and precisely sectioned mineral mounts for in situ chemical analyses—An example using olivine for diffusion chronometry studies

Diffusion chronometry is now a widely applied methodology for determining the rates and timescales of geologic processes from the chemical zoning observed in minerals. Despite the popularity of the method, several challenges still remain during its application, including: (1) the random sectioning of minerals either in thin sections or grain mounts in which both off-center and oblique sections contribute substantial uncertainty to modeled timescales and (2) diffusion anisotropy needs to be accounted for in models, which generally requires determining the principal crystallographic axes of the mineral using electron backscatter diffraction, a technique that is both challenging and limiting because few scanning electron microscopes have an electron backscatter detector. This guide developed by the U.S. Geological Survey focuses on a step-by-step methodology for mounting individually oriented minerals that are sectioned through their cores prior to polishing for analytical work. Using this technique, one can significantly reduce the uncertainties associated with off-center sections and minimize or completely remove the need for determining crystallographic orientation via electron backscatter diffraction analyses. This report is presented as a guide for using the technique on olivine crystals but can be applied to any minerals that can be extracted for analysis. Two variations of the methodology are included here: (1) The individual crystal method that entails mounting individually sectioned single crystals and crystal groups and (2) the whole mount method in which multiple single crystals or crystal clusters are mounted and sectioned at the same time.

Techniques and Methods↗

USGS1984

FEDERAL MINERAL LAND INFORMATION SYSTEM.

The ability of geographic information systems to combine point, line, and areal data has been widely documented, although the establishment of a particular data base presents its own unique problems. The U. S. Geological Survey is developing a geographic information system consisting of information on Federal surface ownership, Federal subsurface mineral rights, location of actual mineral occurrences and (or) known potential, and formal restrictions to mineral development. By utilizing information already compiled or soon to be collected by other agencies, the Federal Mineral Land Information System should be able to provide answers relating to mineral availability on public lands.

Conference Paper↗

USGS1988

COEXISTING GALENA, PbS//S//S AND SULFOSALTS: EVIDENCE FOR MULTIPLE EPISODES OF MINERALIZATION IN THE ROUND MOUNTAIN AND MANHATTAN GOLD DISTRICTS, NEVADA.

Studies of galena and Pb-Bi-Ag-Cu(Hg) sulfosalts of varied compositions in the Round Mountain and Manhattan gold districts of Nevada corroborate the occurrence of several distinct mineralized systems characterized by different mineral compositions and assemblages. The different episodes of mineralization are related to different Cretaceous and Tertiary magmatic-hydrothermal events, although the assignment of specific mineral compositions and associations with dated mineralized systems is still incomplete. At the Fairview mine, galena associated with Pb-Bi-Ag sulfosalts and simple sulfides occurs as intergrowths of discretely different composition controlled by silver and bismuth content. A galena-type phase (Pbs//s//s) with solid solution toward matildite, AgBiS//2(composition Gal//6//0Mat//4//0) was found. If silver and, to a lasser extent, bismuth are absent, the galena formed will be almost pure PbS. Some minor antimony may substitute for bismuth. This study confirms a linear relationship between a cell edge and Ag-Bi(Sb) content for galena containing less than about 15 wt. percent Ag and Bi(Sb).

Canadian Mineralogist↗

USGS1987

ECONOMICS AND THE SEARCH FOR OFFSHORE HEAVY MINERAL DEPOSITS.

This paper examines the relative importance, in terms of a deposit's commercial status, of physical characteristics of onshore titanium-bearing heavy-mineral placer deposits, and applies these findings to the search for and evaluation of offshore deposits. Results obtained by applying statistical discriminant analysis show that the characteristics most useful for predicting a deposit's commercial status are the grades of the constituent titanium minerals and the size of the deposit. Heavy-mineral grade or even the combined grades of all titanium-bearing minerals (without information and constituent mineral grades) are inferior predictors of a deposit's commercial status. When data from homogeneous regions are analyzed separately, the ability to accurately predict the deposit's commerical status improves.

Marine Mining↗

USGS1990

Oxygen and carbon isotope ratios of hydrothermal minerals from Yellowstone drill cores

Oxygen and carbon isotope ratios were measured for hydrothermal minerals (silica, clay and calcite) from fractures and vugs in altered rhyolite, located between 28 and 129 m below surface (in situ temperatures ranging from 81 to 199??C) in Yellowstone drill holes. The purpose of this study was to investigate the mechanism of formation of these minerals. The ??18O values of the thirty-two analyzed silica samples (quartz, chalcedony, ??-cristobalite, and ??-cristobalite) range from -7.5 to +2.8???. About one third of the silica 7samples have ??18O values that are consistent with isotopic equilibrium with present thermal waters; most of the other silica samples appear to have precipitated from water enriched in 18O (up to 4.7???) relative to present thermal water, assuming precipitation at present in situ temperatures. Available data on fluid-inclusion homogenization temperatures in hydrothermal quartz indicate that silica precipitation occurred mostly at temperatures above those measured during drilling and imply that 15O enrichments in water during silica precipitation were generally larger than those estimated from present conditions. Similarly, clay minerals (celadonite and smectite) have ??18O values higher (by 3.5 to 7.9???) than equilibrium values under present conditions. In contrast, all eight analyzed calcite samples are close to isotopic equilibrium with present thermal waters. The frequent incidence of apparent 18O enrichment in thermal water from which the hydrothermal minerals precipitated may indicate that a higher proportion of strongly 18O-enriched deep hydrothermal fluid once circulated through shallow portions of the Yellowstone system, or that a recurring transient 18O-enrichment effect occurs at shallow depths and is caused either by sudden decompressional boiling or by isotopic exchange at low water/rock ratios in new fractures. The mineralogy and apparent 18O enrichments of hydrothermal fracture-filling minerals are consistent with deposition during transient boiling or rock-water exchange (fracturing) events. ?? 1990.

Journal of Volcanology and Geothermal Research↗

USGS1996

Jensenite, Cu 3 Te (super 6+) O 6 .2H 2 O, a new mineral species from the Centennial Eureka Mine, Tintic District, Juab County, Utah

Jensenite, ideally Cu 3 Te (super 6+) O 6 .2H 2 O, is monoclinic, P2 1 /n (14), with unit-cell parameters refined from powder data: a 9.204(2), b 9.170(2), c 7.584(1) Aa, beta 102.32(3) degrees , V 625.3(3) Aa 3 , a:b:c 1.0037:1:0.8270, Z = 4. The strongest six reflections of the X-ray powder-diffraction pattern [d in Aa(I)(hkl)] are: 6.428(100)(101,110), 3.217(70)(202), 2.601(40)(202), 2.530(50)(230), 2.144(35)(331) and 1.750(35)(432). The mineral is found on the dumps of the Centennial Eureka mine, Juab County, Utah, where it occurs as isolated crystals or as groups of crystals on drusy white quartz. Associated minerals are mcalpineite, xocomecatlite and unnamed Cu(Mg,Cu,Fe,Zn) 2 Te (super 6+) O 6 .6H 2 O. Individual crystals of jensenite are subhedral to euhedral, and form simple rhombs that are nearly equant. Some crystals are slightly elongate [101], with a length-to-width ratio up to 2:1. The largest crystal is approximately 0.4 mm in size; the average size is between 0.1 and 0.2 mm. Cleavage {101} fair. Forms are: {101} major; {110} medium; {100} minor; {301}, {201}, {203}, {102}, {010} very small. The mineral is transparent, emerald green, with a less intense streak of the same color and an uneven fracture. Jensenite is adamantine, brittle and nonfluorescent; H (Mohs) 3-4; D (calc.) 4.78 for the idealized formula, 4.76 g/cm 3 for the empirical formula. In a polished section, jensenite is very weakly bireflectant and nonpleochroic. In reflected plane-polarized light in air, it is a nondescript grey, and in oil, it is a much darker grey in color with a brownish tint, with ubiquitous bright green internal reflections. Anisotropy is not detectable. Measured values of reflectance, in air and in oil, are tabulated. Electron-microprobe analyses yielded CuO 50.91, ZnO 0.31, TeO 3 38.91, H 2 O (calc.) [8.00], total [98.13] wt.%. The empirical formula, derived from crystal-structure analysis and electron-microprobe analyses, is (Cu (sub 2.92) Zn (sub 0.02) ) (sub Sigma 2.94) Te (super 6+) (sub 1.01) O (sub 5.97) .2.03H 2 O, based on O = 8. The mineral name honors Martin C. Jensen, Reno, Nevada, who discovered the mineral.

Canadian Mineralogist↗

USGS2008

Hepatic minerals of white-tailed and mule deer in the southern Black Hills, South Dakota

Because there is a paucity of information on the mineral requirements of free-ranging deer, data are needed from clinically healthy deer to provide a basis for the diagnosis of mineral deficiencies. To our knowledge, no reports are available on baseline hepatic mineral concentrations from sympatric white-tailed deer (Odocoileus virginianus) and mule deer (Odocoileus hemionus) using different habitats in the Northern Great Plains. We assessed variation in hepatic minerals of female white-tailed deer (n=42) and mule deer (n=41). Deer were collected in February and August 2002 and 2003 from study areas in Custer and Pennington Counties, South Dakota, in and adjacent to a wildfire burn. Hepatic samples were tested for levels (parts per million; ppm) of aluminum (Al), antimony (Sb), arsenic (As), barium (Ba), boron (B), cadmium (Cd), calcium (Ca), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), magnesium (Mg), manganese (Mn), mercury (Hg), molybdenum (Mo), nickel (Ni), phosphorus (P), potassium (K), selenium (Se), sodium (Na), sulfur (S), thalium (T1), and zinc (Zn). We predicted that variability in element concentrations would occur between burned and unburned habitat due to changes in plant communities and thereby forage availability. We determined that Zn, Cu, and Ba values differed (P???0.05) between habitats. Because of the nutritional demands of gestation and lactation, we hypothesized that elemental concentrations would vary depending on reproductive status; Cd, Cu, Ca, P, Mn, Mo, Na, and Zn values differed (P???0.05) by reproductive status. We also hypothesized that, due to variation in feeding strategies and morphology between deer species, hepatic elemental concentrations would reflect dietary differences; Ca, Cu, K, Co, Mo, Se, and Zn differed (P???0.05) between species. Further research is needed to determine causes of variation in hepatic mineral levels due to habitat, reproductive status, and species. ?? Wildlife Disease Association 2008.

Journal of Wildlife Diseases↗

USGS2005

Mineral resources and consumption in the twenty-first century

Modern societies are highly dependent upon energy and mineral resources to produce and deliver the material goods and even the services of everyday life. Although societies' dependence upon fossil fuels is evident and understood by much of the population, few people are as well informed about their dependence upon a wide variety of nonfuel minerals. This ignorance may result from two interrelated conditions. First, in contrast to fossil fuels, few people directly use nonfuel minerals in recognizable forms because most use is as part of manufactured products. Second, the value of raw ($38 billion) and even processed ($397 billion) nonfuel minerals in the United States in 2002 was small relative to the value the industries that consume these materials contribute to the economy ($1,700 billion). That is, although nonfuel mineral inputs are indispensable to construction and to the manufacture of durable and even nondurable goods (USGS 2003), their value is modest compared with the value of the final products.

Book chapter↗

USGS2015

Ocean minerals

Nearly 71 percent of the Earth is covered by ocean, yet during the entire history of societies, the mineral resources essential for nation building have been acquired solely from the continents. Deep-ocean minerals were discovered over a century ago during the Challenger expedition of 1873—1876, but only relatively recently did programs develop to determine their origin, distribution, and resource potential. Continental margin marine mineral deposits include aggregate, sand, placer minerals, and phosphorite. Aggregate, sand, and placers are detrital minerals that were transported and deposited on the shelf, whereas phosphorite is a chemical sedimentary deposit that formed in place from chemical reactions in the near-surface sediment. Seawater makes up 98.8 percent of the world's surface water and contains every element in the periodic table, mostly in trace concentrations. Fe-Mn crusts are found on rock surfaces of seamounts, ridges, and plateaus as pavements and coatings on talus in areas that remain sediment-free for millions of years.

Book chapter↗

USGS2015

Mapping surficial minerals at high latitudes: The USGS 2014 imaging spectrometer data collection in Alaska

Passive optical remote sensing of high latitude regions faces many challenges including a short acquisition season and poor illumination due to low solar elevation. Additional complications are encountered in the identification of surface minerals for mineral resource characterization because minerals of interest commonly are exposed on steep terrain, further challenging reflectance retrieval and detection of mineral signatures. On shallow slopes and flat terrain, vegetation cover can interfere with or obscure the absorption features of minerals in rock and soil. The USGS is conducting a study to examine the viability of using remote sensing techniques for identification of large-tonnage, base metal-rich deposits in Alaska.

Alaska↗

USGS2014

Mineral resource of the month: vermiculite

Vermiculite comprises a group of hydrated, laminar magnesium-aluminum-iron silicate minerals resembling mica. They are secondary minerals, typically altered biotite, iron-rich phlogopite or other micas or clay-like minerals that are themselves sometimes alteration products of amphibole, chlorite, olivine and pyroxene. Vermiculite deposits are associated with volcanic ultramafic rocks rich in magnesium silicate minerals, and flakes of the mineral range in color from black to shades of brown and yellow. The crystal structure of vermiculite contains water molecules, a property that is critical to its processing for common uses. Using a process called exfoliation-in which vermiculite flakes are heated to 900 degrees Celsius or higher, causing water within the flakes to flash to steam and expand-crude vermiculite ore is processed into particles that are eight to 20 times larger. The resulting lightweight material is chemically inert and fire resistant, with low density and low thermal conductivity. It is also odorless, has high liquid absorption capacity and catalytic properties. Because it is lightweight and thermally insulating, vermiculite is used in general building plasters and concrete products, alone or combined with other lightweight aggregates such as perlite. Special plasters, in which vermiculite is combined with binders like gypsum or portland cement, fillers or other additives, provide fire protection and soundproofing. As insulation, exfoliated vermiculite, sometimes treated with a water repellent, is used to fill pores and cavities in masonry construction and hollow blockwork to enhance acoustic properties, fire rating and insulation performance. Exfoliated vermiculite can also be used to produce refractory and insulation concretes and mortars, and to make high-temperature binders for construction materials, gaskets, specialty papers, textiles and vehicle brake linings. Finer grades of exfoliated vermiculite can be used to produce various shapes of insulation pellets, high-temperature insulation, as a primary component in cementitious coatings, and as a filler in inks, paints, plastics and other materials. Vermiculite can absorb liquids such as fertilizers, herbicides and insecticides, which can then be transported as free-flowing solids. It is used in the fertilizer and pesticide markets because of its ability to act as a bulking agent, carrier and extender. In horticulture, exfoliated vermiculite improves soil aeration and moisture retention, and when mixed with peat or other composted materials, such as pine bark, vermiculite produces a good growing medium for plants. As a soil conditioner, exfoliated vermiculite improves aeration in clay-rich soils and water retention in sandy soils, while reducing the likelihood of compaction, cracking and crusting of the soil. For more information on the commercial use of vermiculite, visit minerals.usgs.gov/minerals/ .

Earth↗