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At least 577 records · Page 32Linked to original sources
USGS1936

Hydrothermal leaching in the Virginia mining district, New Mexico

The tourmaline-copper deposits of the Virginia mining district, New Mexico, lie along veins that were plugged and reopened repeatedly during the process of mineral deposition. At some time between the second and third stages of deposition the solutions removed calcite, sericite, and chlorite from interstitial and included fragments of altered wall-rock in the veins and thereby produced honeycombed box-works of first- and second-stage minerals, chiefly specularite, quartz, and chalcopyrite, on the walls of which minerals of later stages were deposited. It is suggested that the leaching solutions may have been acid and that the leaching was done by the fresh solutions of the third stage before their acidity was neutralized through reactions along their channelways. A mechanism is suggested to account for their presence at places previously traversed by alkaline or neutral solutions.

New Mexico↗
USGS1936

Nodular, orbicular, and banded chromite in northern California

IN I930 Mr. A. F. Duggleby gave me a specimen of orbicular chromite from the Octopus claim, in Siskiyou County, Calif., showing two generations of chromite, one older than the associated olivine and one younger. In November, I93I, I examined briefly a number of deposits in northern California, in search for chromite showing similar and related textures. Some of the more unusual and genetically significant occurrences are described in this paper. Most of the chromite localities here described are in Siskiyou County, northern California. Localities I and 2 are in the Seiad Quadrangle, where a belt of chromite-bearing dunite, striking northwest, extends from McGuffy Creek, near Scott Bar, into Oregon. Other deposits are in southern Siskiyou, Shasta, and Trinity Counties.

Economic Geology↗
USGS1937

Origin of the bedding replacement deposits of fluorspar in the Illinois field

The banded fluorspar deposits of the Cave In Rock district are attributed to replacement of limestone and the preservation of bedding and cross-bedding of the rock. The solutions contained hydrofluoric acid which reacted with CaCO 3 . The replacement was stoichiometrical, with consequent reduction of volume, but continued deposition of calcium fluoride, brought in from other points, partly or completely filled the voids. Thus, the pure bands display a comb structure, and represent replacement of pure limestone laminae. The less pure granular bands, devoid of comb structure, reflect the alternating, impure bands of the rock in which the fine-grained impurities (ferriferous carbonate, clay, et al) were disseminated. Recrystallization of clastic quartz grains in some calcareous sandstone layers resulted in the formation of bands of quartz grains. The writer dissents from the views of Bastin who believes the banding is due to rhythmic precipitation. Chemistry and controlling structural conditions are discussed.

Illinois↗
USGS1938

Some mineral deposits of Glacier Bay and vicinity, Alaska

Prospecting in the Glacier Bay National Monument has been confined so far to granitic rocks near contacts with Paleozoic sediments, which they intrude.Near Reid Glacier thin veins, a few of which are traceable for about 300 feet both horizontaliy and vertically, trend northerly and carry sphalerite, galena, and pyrite. Gold was panned from some of the better looking material.Near Sandy Cove, 30 miles away, more irregular, but locally thicker, veins appear to carry only pyrite. Here pyrite also occurs along the contact between the granitic rocks and the intruded limestone.Sparse ore minerals have been seen at other places in and near the monument. As yet, no large mineral deposits have been found there, but many miles of igneous contacts have not been prospected. In southeastern Alaska, as elsewhere, such contacts are considered favorable places in which to search for mineral deposits.

Alaska↗
USGS1938

Outlook for further ore discoveries in the Little Hatchet Mountains, New Mexico

The Little Hatchet Mountains contain two mining districts, the Eureka silver-lead-zinc district and the Sylvanite gold district, the deposits of each being associated with a mass of monzonite that intrudes Lower Cretaceous sediments. The same formations crop out in both districts, having been duplicated by a large post-ore fault, and the two monzonite masses and their accompanying mineralized zones lie at essentially the same stratigraphic position in the two fault blocks. The deposits of the Eureka district are mesothermal whereas those of the Sylvanite district are hypothermal, but the two groups are mineralogically similar in many respects.As the two monzonite exposures are several miles apart, the natural inference is that there are two separate intrusions. Contrary to this inference, the evidence of structure, mineralogy, and petrology indicates that the two monzonite masses are faulted parts of the same body and that the mineralized areas of the Eureka and Sylvanite districts were originally continuous and zonally related, the original igneous mass having been a flat-lying sill-like streamer, 7 miles or more long, that was bordered by a contact-metamorphic halo and that formed the core of a zone of mineralization.The economic implications of this interpretation are three-fold: (1) the mineralized zone is limited in thickness and is restricted, like a bedded deposit, to a particular sedimentary horizon; (2) the area between the Eureka and Sylvanite districts, hitherto considered barren, should contain mineralized ground at variable depths below the surface; and (3) the deposits change along the trend of the zone from the gold deposits of the one district to the silver-bearing base-metal deposits of the other. In structure and size the deposits in the hidden parts of the mineralized zone probably are similar to those already known. Under the alternative interpretation that the two districts are separate centers of activity, the outlook for future successful prospecting depends upon the depths at which the underlying Paleozoic limestones lie and the possibility of large deposits having been formed in them.

New Mexico↗
USGS1938

Manganese deposits of the Drum Mountains, Utah

More than 15,000 tons of manganese ore has been produced from small deposits in the Drum Mountains in west-central Utah. Lenses of rhodochrosite, now largely weathered near the surface to manganese oxides, lie parallel to the bedding of Cambrian dolomites and shales near faults that are nearly normal to bedding. Two varieties of rhodochrosite, one fine-grained, dark-gray or black, and massive, the other coarser-grained, pink, and generally occurring in veinlets in the gray variety, are present. The gray contains less MnCO 3 and FeCO 3 , but more CaCO 3 and MgCO 3 than the pink variety. The deposits are interpreted as bodies that replaced favorable dolomite or limestone beds. The gray rhodochrosite first replaced the dolomite or limestone; the pink variety later formed veinlets in the gray rhodochrosite and replaced it to a small extent.

Utah↗
USGS1938

Dolomite and jasperoid in the Metaline District, northeastern Washington

The replacement ore bodies of the Metaline zinc-lead district, in northeastern Washington are limited to the greatly disturbed fault block through which the Pend Oreille River flows and are associated with the major faults but are not in them. They are mostly near the top of the Metaline limestone, of Middle Cambrian age, and below black Ordovician slate. The ores are generally in jasperoid and are surrounded by a shell of crystalline dolomite. Outside of the dolomite is a shell of coarse-grained calcite that in places was deposited along solution channels long distances from known ore bodies. Jasperoid, crystalline dolomite, and, to a less extent, coarse-grained calcite are therefore favorable but not infallible signs of the presence of ore nearby. The Metaline limestone was dolomitized regionally before the ore was introduced, and this early dolomitization is independent of the ore.

Washington↗
USGS1938

Sulphate minerals of the Comstock Lode, Nevada

Seventeen representative samples of supergene sulphates from old workings on the Comstock Lode are described. They range from simple minerals such as gypsum and epsomite to complex aggregates of four or more distinct species. All are well known species except a mineral of the copper (chalcanthite) or magnesium sulphate pentahydrate group, with about half the magnesium replaced by copper, zinc, ferrous iron, and manganese. Four new analyses of Comstock Lode mine waters are given. © 1938 Society of Economic Geologists, Inc.

Nevada↗
USGS1938

The significance and nature of the cone of depression in ground-water bodies

In nature the hydraulic system in an aquifer is in balance; the discharge is equal to the recharge and the water table or other piezometric surface is more or less fixed in position. Discharge by wells is a new discharge superimposed on the previous system. Before a new equilibrium can be established water levels must fall throughout the aquifer to an extent sufficient to reduce the natural discharge or increase the recharge by an amount equal to the amount discharged by the well. Until this new equilibrium is established water must be withdrawnfrom storage in the aquifer and conversely the new equilibrium cannot be established until an amount of water is withdrawn from storage by the well sufficient to depress the piezometric surface enough to change the recharge or natural discharge the proper amount. The depression of the piezometric surface is called the cone of depression.The characteristics of the cone of depression in an idealized aquifer of infinite areal extent are considered mathematically. Time is an essential variable in the description of this cone. The time rate of lateral growth of the cone is independent of the rate of discharge by the well and depends only on the physical characteristics of the aquifer. The cone must grow laterally much more rapidly in artesian aquifers than it does in nonartesian. The characteristics of the cone in actual aquifers are then considered. In finely porous artesian aquifers the cone appears to be much like the cone in the ideal aquifer. The cone in non-artesian aquifers must be somewhat warped. The theory out-lined implies that well discharge from extensive water-table aquifers must be a draft on storage in the aquifer for many generations.

Economic Geology↗
USGS1939

Sienna ("ocher") deposits of the Cartersville District, Georgia

Sienna ("ocher") deposits in the Cartersville district, Georgia, occur in the contact zone between dolomitic limestone and underlying quartzite of Lower Cambrian age. These rocks, together with interbedded schists, were folded and recrystallized probably near the close of Paleozoic time. Simple fissures and transverse and oblique faults, formed during the late stages of folding, admitted hydrothermal solutions, which deposited concentrated masses of hematite and pyrite, and other ore minerals, in the dolomites and calcareous schists. There is some evidence that large bodies of iron carbonate also were deposited. Subsequent weathering has removed the dolomite near the surface, and its residuum in many places rests upon the more resistant quartzite. Iron derived from the hematite and pyrite, and possibly from iron carbonate, was transferred by meteoric waters and deposited as hydrous oxides by partial replacement of (1) irregular, structureless bodies of the residuum, and (2) irregular areas in schists both at the base of the dolomite and beneath the uppermost quartzite bed. A relatively thin superficial portion of the uppermost quartzite bed also was replaced. Transfer of the iron has taken place over short distances only, and the present positions of the sienna deposits reflect essentially the positions of the deposits of source minerals.

Georgia↗
USGS1939

Manganese in a thermal spring in west-central Utah

The hot spring north of Delta, Utah, is of particular interest because it has yielded commercial manganese ore; 715 tons of manganese oxide ore that averaged 20% manganese and 0.26% sulphur is recorded. The deposits occur as a thin bed and as lenses and nodules in a dome about 1,600 feet across and 15 feet high that has been formed subsequent to the dessication of Pleistocene Lake Bonneville. The alkaline hot waters, which reach temperatures of 182 degrees F. and have a total discharge of over 1,200 gallons a minute, average 3,900 parts per million in dissolved solids, with NaCl, CaSO 4 , MgCl 2 , and CaCO 3 . Five complete analyses show a manganese content of from 0 to 1.2 parts per million. Nevertheless, no appreciable manganese seems to be precipitating at present. The bed of manganese and iron oxides is scarcely more than a foot thick and is mostly covered by porous calcite. The ore is a porous aggregate of psilomelane and pyrolusite in which the vugs are lined with limonite. These minerals have been formed through the action of hot alkaline solutions over a long period; the original mineral was probably wad. The barium oxide is believed to be chemically combined with the manganese oxides. Probably all these materials have been leached from underlying rocks or deposits by hot circulating groundwaters and may not have a magmatic source.

Utah↗
USGS1940

The Vaucluse gold mine, Orange County, Virginia

The Vaucluse gold property has been worked intermittently since gold was discovered in 1832. The latest operation was carried on by the V-M Corporation from March 1935 to November 1938, producing 26,452 tons of ore of \$143,760 gross value, of which \$91,569.36 was won in 1938. The host rock is a quartz-sericite-chlorite schist. The workings lie wholly within a well-defined shear zone up to 40 feet in width, which has been traced along the surface for several miles. The shear zone strikes N. 40 degrees -60 degrees E. and is conformable with the schistosity of the enclosing rock. The ore is in shoots that pitch NE. at angles ranging between 30 degrees and 70 degrees and conform to fluting in the shear zone. The ore occurs along the walls of the shear zone and the location of the shoots was controlled, partly at least, by pre-mineral fractures. Quartz, sericite, and ankerite make up most of the gangue and chlorite is abundant in the enclosing rock. Abundant pyrite is the only important sulphide; some chalcopyrite and galena are generally present. Gold is the only mineral of economic value and is intimately associated with the pyrite. The ore was milled on the property and flotation concentrates were shipped to a smelter. Direct mining, milling, and shipping cost per ton, from December 1935 to November 1938, was $4.56. Approximately 4,500 feet of core drilling was done below the 300-foot level, which indicated about the same conditions as those present above this level.

Virginia↗
USGS1940

Phosphate deposits of the United States

Different types of phosphate deposits and different sources of phosphate in the United States are briefly discussed. In Florida two types of phosphate are now mined, land pebble and hard rock. The principal characteristics of these types of rock are stated and methods of prospecting, mining and recovery briefly outlined. Testimony given before the Congressional Committee to Investigate the Adequacy and Use of Phosphate Resources of the United States, November 28, 1938, at Lakeland, Fla., showed Florida's reserves to be far greater than previously supposed. Similarly at corresponding hearings in Tennessee a few days earlier the reserves of brown phosphate, the only type now mined in that State, were shown to exceed earlier official estimates. Reserves of the Western fields have been raised a little to bring them abreast of current information but no attempt has been made, as in the other States named, to include lower grades of rock than those formerly considered in the estimates. Professor J. Stewart Williams has shown for Utah that such a procedure would tremendously increase these figures . Reserves of the United States as a whole are now considered to exceed ten billion tons, not counting those classed as possible or certain phosphatic limestones mentioned at the hearings of the Congressional Committee. As nearly 2,000,000 acres of public land in the Western States and 66,000 acres in Florida remain to be examined for their phosphate content the stated figure will ultimately be greatly increased. At the present rate of consumption, 3,000,000 tons annually, ten billion tons would last more than 3,000 years.

Colorado, Florida, Idaho, Montana, South Carolina,↗
USGS1941

The quicksilver deposits of the Terlingua region, Texas

Texas is second among quicksilver-producing States because of the Terlingua region, in the Big Bend of the Rio Grande. This region contains Cretaceous strata, largely calcareous, which grade upward into Tertiary volcanics, locally without break. The strata are cut by numerous intrusions, largely alkalic, and are extensively folded and faulted.Many of the lodes are near the base of the impervious Del Rio clay, some at higher horizons, and a few in intrusive masses. The solutions penetrated only along open passageways, such as major fractures or joints in zones of tension, and, especially at horizons above the Del Rio, in fractures related to fault zones.The quicksilver is believed to have been brought in by alkali sulphide solutions. Most other constituents that may once have been present in the solutions had been separated earlier. Precipitation resulted largely from mingling with groundwater. The comparatively low temperature and pressure at the shallow levels where groundwater was present aided the precipitation. As the then-existing zone of groundwater circulation has since been partly exposed by erosion, the lodes are necessarily rather close to the present surface. The gangue minerals, particularly the calcite, are believed to have been derived mainly from the sedimentary rocks with some addition of material from deep sources. The relation of the widespread bitumen to genesis is puzzling here, as in many other quicksilver deposits. Weathering is of slight economic importance. Many minerals that resemble supergene products, including the quicksilver chlorides, are thought to have resulted here from original deposition within the zone of vadose water.

Texas↗