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USGS1954

The gold pan: A neglected geological tool

The gold pan is ordinarily regarded as a tool for sampling placer deposits. Another and very important application is shown to be the sampling and study of decomposed bedrock, in regions where outcrops of hardrock are scarce or lacking. This technique was proposed and used by Derby, an American geologist who worked for many years in Brazil. The importance of this method has not been generally recognized, and the writer recalls it to the attention of geologists. An important application is shown to exist in the study of the decomposed bedrock, known as saprolite, that is so widespread in the Piedmont province of the southeastern United States. Using this technique, two projects have already been successfully completed in this region, and the success attained in both sets a new standard for geological exploration and mapping in areas where saprolite constitutes the dominant type of exposure. The technique of panning for heavy and semiheavy accessory minerals is described. Types of pans, factors in panning, the operation of panning, and the processing of concentrates in the field are briefly discussed. The gold pan, in the hands of an experienced operator, is shown to be a versatile and efficient field tool, which is completely independent of laboratory facilities. © 1954 Society of Economic Geologists, Inc.

Economic Geology↗

USGS1997

Epithermal mercury-antimony and gold-bearing vein lodes of southwestern Alaska

Epithermal mineral deposits and occurrences of southwestern Alaska consist of Hg-Sb and gold- and sulfide-bearing vein lodes. Numerous Hg-Sb lodes are located throughout a region measuring several tens of thousands of square kilometers in and surrounding the Kuskokwim River basin in southwestern Alaska. The Hg-Sb lodes are hosted in sedimentary rocks of the Cretaceous Kuskokwim Group, the Triassic to Cretaceous Gemuk Group, and the Paleozoic Holitna Group, as well as in Late Cretaceous and early Tertiary mafic to felsic intrusive rocks. Mineralized Hg-Sb vein and vein breccia lodes are found in the sedimentary or igneous rocks or at their contacts. The minerology of the Hg-Sb lodes is dominated by cinnabar and stibnite, with subordinate realgar, orpiment, and native mercury, pyrite, gold, and hematite, as well as solid and liquid hydrocarbons; quartz, carbonate, limonite, dickite, and sercite are alteration gangue minerals. The largest mercury mine in Alaska, Red Devil, produced about 36,000 flasks of mercury, but the Hg-Sb lodes of southwestern Alaska generally consist of small, discontinuous veins that rarely exceed a few meters in width and a few tens of meters in strike length. The Hg-Sb lodes generally contain about 1 to 5 percent Hg and less than 1 percent Sb and As but are generally poor in base emtals and precious metals. Anomalous concentrations of gold in some lodes, however, suggest that gold deposits may be present in higher temperature environments below some of the Hg-Sb lodes. The formation of the Hg-Sb lodes is closely correlated with igneous activity of a Late Cretaceous and early tertiary magmatic arc in southwestern Alaska. Geologic and geochemical characteristics of the Hg-Sb lodes suggest that ore fluids were generated in local sedimentary rocks as they were intruded by magmas. These intrusions provided the heat to initiate dehydration reactions and expel fluids from hydrous minerals and formational waters in the sedimentary rocks, causing thermal convection and hydrothermal fluid flow along fractures and faults. Isotopic data from sulfide and alteration minerals of the Hg-Sb lodes indicate multiple sources for the ore fluids; most fluids appear to have originated from local sedimentary rocks. Hydrothermal fluids with isotopically heavy oxygen but isotopically light hydrogen and sulfur compositions indicate derivation of these species from sedimentary rocks. Isotopically shifted, evolved meteoric water was a primary component in ore fluids from a few Hg-Sb lodes. Geochemical, isotopic, and fluid inclusion data also indicate that Hg, Co 2 , CH 4 , N2, and local hydrocarbons were derived from breakdown of organic matter in sedimentary rocks when they were heated by intrusions. Radiometric 40 Ar/ 39 Ar ages of 70 ± 3 Ma from hydrothermal sercites in the Hg-Sb lodes indicate a temporal association of igneous activity and mineralization, which is consistent with the geologic characteristics. Most epithermal gold-bearing vein lodes on the Alaska Peninsula and Aleutian Islands are located in Eocene to Pleistocene volcanic-arc rocks, commonly andesite and dacite. These vein and vein breccia lodes, such as the Alaska-Apollo and Shumagin deposits on Unga Island, tend to be aligned along regional, northeast-striking, steeply dipping faults and fractures. The Alaska-Apollo mine produced about 500,000 metric tons (t) of ore that yielded an estimated 3,500 kg (130,000 oz) of gold from veins that were as much as 12 m wide and extended for 1,500 m laterally and 420 m vertically. Ore minerals include gold, galena, sphalerite, chalcopyrite, pyrite, marcasite, arsenopyrite, and native copper; gangue minerals are quartz, sericite, calcite, and chlorite and locally, barsite, clay, rhodonite, and adularia. Ores generally have Au-Ag-Te-Pb-Zn-Mn-Cu geochemical signatures, with wide As-Hg aureoles around some veins. Geologic and mineralogical characteristics of these lodes are similar to adularia-sericite volcanic-hosted epithermal deposits. The gold-bearing vein lodes may be related to arc porphyry systems, but more data are required to verify this association.

Alaska↗

USGS1983

Airborne biogeophysical mapping of hidden mineral deposits

Airborne survey techniques have been developed to detect and map forest canopies affected by metal-induced stress. A high spectral resolution airborne spectroradiometer system, used over a known forest-covered copper soil anomaly, has revealed previously unknown spectral changes in the near-infrared chlorophyll absorption spectrum. The metal-induced spectral shifts have subsequently been reproduced in the laboratory at Columbia University. Waveform analysis techniques specifically designed for computer analysis of the high spectral resolution aircraft data filter out the very strong background noise introduced by variations in normal, unstressed vegetation canopy and by topographic effects. The wave-form method proves most effective in extracting the subtle spectral indicators of metal-induced stress. The analytic method is a unique frequency domain technique made possible by the high spectral resolution of the 500-channel spectroradiometer system. The biogeophysical technique is demonstrated by three mapping surveys of Cotter Basin, Montana, and Spirit Lake, Washington. This airborne mapping technique presents new application opportunities in large areas of the world where heavy forest cover has in the past made geologic and geophysical exploration tedious and expensive. The tree cover with widespreading and deeply penetrating root systems is turned to an advantage in the airborne biogeophysical technique by detecting metal-induced changes in the chlorophyll reflectance spectrum.

Montana↗

USGS1943

Quartz veins in the Ouachita mountains of Arkansas and Oklahoma (Their relations to structure, metamorphism, and metalliferous deposits)?

An important chapter of the total geologic history of the Ouachita Mountains is revealed by the quartz veins and crystals. These and the associated minerals are hydrothermal deposits of probable magmatic origin, formed during the closing stage of the mid-Permsylvanian orogeny. The metalliferous deposits of the Ouachita Mountains appear to have been formed at the time of the quartz vein deposition. This /act should be considered in dating the lead and zinc mineralization in other areas of the Mississippi Valley region. © 1943 Society of Economic Geologists, Inc.

Arkansas, Oklahoma↗

USGS1937

Isometric block diagrams in mining geology

In the past five years members of the Geological Survey have gained experience in making isometric block diagrams of mines and mining districts as well as of surface features. This paper presents nothing new, but aims to assemble scattered information on a much neglected method of geological illustration. Plotting mine workings on isometric paper is the usual method but is extremely time-consuming. For most purposes the use of some form of isometric pantograph greatly lessens the labor of constructing the diagram. The devices of Dufour, Wentworth, Wilson, and Van der Hoop are described

Economic Geology↗

USGS1971

Coronadite — Modes of occurrence and origin

The lead manganate, "coronadite," was first recognized at the Coronado mine in the Morenci district, Arizona, by Lindgren in 1903. Several years later, the identity of the mineral was questioned and it was not until 1932 that Orcel recognized it in material from Morocco. Since 1955, the mineral has been recognized at numerous places; in the USSR, east of the Ural Mountains, in several districts in Morocco, England, Australia, and India. In recent years, coronadite had been identified at numerous localities in New Mexico, Arizona, Nevada, and California by the writer and others. At this time, it has been identified at 22 localities, and in the opinion of this writer, it will be found at many more places if it is sought for carefully. Author's review of the known occurrences of coronadite and interpretation of the modes of geologic environment show that the mineral is found in veins and hot spring aprons, where it seems to have been deposited by hydrothermal waters from depth and that it is one of the manganese oxide minerals deposited as sediments. Probably it is more widely found in assemblages of minerals of supergene origin.

Arizona, Asturias, California, Chihuahua, Durango,↗

USGS1940

Geology and ground-water resources of the "Equus beds" area in south central Kansas

This paper summarizes the results of a detailed investigation by the U. S. Geological Survey in cooperation with the Kansas State Geological Survey, Kansas State Board of Health, and the City of Wichita. The geology of the area has been remapped, and several new formations have been established, including the Emma Creek formation of middle and upper Pliocene age, and a thick loess deposit. The hydrologic studies involved extensive test drilling and resulted in the development of a new groundwater supply for the City of Wichita.

Kansas↗

USGS1986

Quantitative estimation of undiscovered mineral resources: A case study of US Forest Service Wilderness tracts in the Pacific Mountain system

The need by land managers and planners for more quantitative measures of mineral values has prompted scientists at the U.S. Geological Survey to test a probabilistic method of mineral resource assessment on a portion of the wilderness lands that have been studied by the Survey during the past 20 years. A quantitative estimate of undiscovered mineral resources is made by linking the techniques of subjective estimation, geologic mineral deposit models, and Monte Carlo simulation. The study, which uses grade-tonnage and occurrence models for 21 geologic deposit types, considers 91 U.S. Forest Service wilderness tracts in California, Nevada, Oregon, and Washington. Estimates of the amounts of the 11 metals contained in undiscovered mineral deposits of the types studied range from negligible to several years of U.S. consumption. Although these estimates are limited to metals contained in undiscovered deposits of a small number of metallic mineral deposit types, the assessment procedure can be expanded by the use of additional deposit models and by using information about identified mineral resources. This will allow models of economic processes such as exploration, development, and production to be applied.

Economic Geology↗

USGS2004

40 Ar/ 39 Ar Dating of Zn-Pb-Ag Mineralization in the Northern Brooks Range, Alaska

The 40 Ar/ 39 Ar laser step-heating method potentially can be used to provide absolute ages for a number of formerly undatable, low-temperature ore deposits. This study demonstrates the use of this method by determining absolute ages for Zn-Pb-Ag sediment-hosted massive sulfide deposits and vein-breccia occurrences found throughout a 300-km-long, east-west-trending belt in the northern Brooks Range, Alaska. Massive sulfide deposits are hosted by Mississippian to Pennsylvanian(?) black carbonaceous shale, siliceous mudstone, and lesser chert and carbonate turbidites of the Kuna Formation (e.g., Red Dog, Anarraaq, Lik (Su), and Drenchwater). The vein-breccia occurrences (e.g., Husky, Story Creek, West Kivliktort Mountain, Vidlee, and Kady) are hosted by a deformed but only weakly metamorphosed package of Upper Devonian to Lower Mississippian mixed continental and marine clastic rocks (the Endicott Group) that stratigraphically underlie the Kuna Formation. The vein-breccias are mineralogically similar to, but not spatially associated with, known massive sulfide deposits. The region's largest shale-hosted massive sulfide deposit is Red Dog; it has reserves of 148 Mt grading 16.6 percent zinc, 4.5 percent lead, and 77 g of silver per tonne. Hydrothermally produced white mica in a whole-rock sample from a sulfide-bearing igneous sill within the Red Dog deposit yielded a plateau age of 314.5 Ma. The plateau age of this whole-rock sample records the time at which temperatures cooled below the argon closure temperature of the white mica and is interpreted to represent the minimum age limit for massive sulfide-related hydrothermal activity in the Red Dog deposit. Sulfide-bearing quartz veins at Drenchwater crosscut a hypabyssal intrusion with a maximum biotite age of 337.0 Ma. Despite relatively low sulfide deposition temperatures in the vein-breccia occurrences (162°-251°C), detrital white mica in sandstone immediately adjacent to large vein-breccia zones was partially to completely recrystallized. The 40 Ar/ 39 Ar age spectra and inverse isochron plots of the multicomponent whole-rock sandstone samples are more complex than those of single minerals. However, different minerals have different Ca/K and Cl/K ratios and closure temperatures, and these properties were used to identify portions of spectra dominated by argon release from specific minerals. 40 Ar/ 39 Ar laser step-heating analyses of Late Devonian sandstone whole rocks produced spectra that record a two-stage resetting history: a Carboniferous hydrothermal event first and later Mesozoic to Tertiary events, which are in agreement with geologic constraints. The 40 Ar/ 39 Ar ages and the similar mineralogy, lead isotope composition, and relative stratigraphic positions support the interpretation that the shale-hosted massive sulfide deposits and most vein-breccia occurrences are temporally and genetically related, and that they are different expressions of Carboniferous basinal dewatering.

Alaska↗

USGS1988

Age of native copper mineralization, Keweenaw Peninsula, Michigan

Amygdaloidal flood basalts and conglomerates are the host for substantial deposits of native copper within the Portage Lake Volcanics in the Keweenaw Peninsula of Michigan. A wide variety of gangue minerals are associated with the regional hydrothermal alteration-mineralization event. Application of the Rb-Sr method to amygdule-filling microcline, calcite, epidote, and chlorite suggests an age of mineralization between 1,060 and 1,047 m.y. (+ or - [asymp] 20 m.y.). These results are supported by a fission track age on epidote of 1,044 + or - 169 m.y. The age of native copper mineralization determined in this study is consistent with geologic evidence which suggests that mineralization postdated the deposition of most or all of the overlying Freda Sandstone. Variable initial 87 Sr/ 86 Sr ratios between the low Rb/Sr phases suggest mixing of isotopically distinct sources of Sr during the generation and equilibration of the hydrothermal solutions.

Michigan↗

USGS1997

Precious metals associated with Late Cretaceous-early Tertiary igneous rocks of southwestern Alaska

Placer gold and precious metal-bearing lode deposits of southwestern Alaska lie within a region 550 by 350 km, herein referred to as the Kuskokwim mineral belt. This mineral belt has yielded 100,240 kg (3.22 Moz) of gold, 12, 813 kg (412,000 oz) of silver, 1,377,412 kg (39,960 flasks) of mercury, and modest amounts of antimony and tungsten derived primarily from the late Cretaceous-early Tertiary igneous complexes of four major types: (1) alkali-calcic, comagmatic volcanic-plutonic complexes and isolated plutons, (2) calc-alkaline, meta-aluminous reduced plutons, (3) peraluminous alaskite or granite-porphyry sills and dike swarms, and (4) andesite-rhyolite subaerial volcanic rocks. About 80 percent of the 77 to 52 Ma intrusive and volcanic rocks intrude or overlie the middle to Upper Cretaceous Kuskokwim Group sedimentary and volcanic rocks, as well as the Paleozoic-Mesozoic rocks of the Nixon Fork, Innoko, Goodnews, and Ruby preaccretionary terranes. The major precious metal-bearing deposit types related to Late Cretaceous-early Tertiary igneous complexes of the Kuskokwim mineral belt are subdivided as follows: (1) plutonic-hosted copper-gold polymetallic stockwork, skarn, and vein deposits, (2) peraluminous granite-porphory-hosted gold polymetallic deposits, (3) plutonic-related, boron-enriched silver-tin polymetallic breccia pipes and replacement deposits, (4) gold and silver mineralization in epithermal systems, and (5) gold polymetallic heavy mineral placer deposits. Ten deposits genetically related to Late Cretaceous-early Tertiary intrusions contain minimum, inferred reserves amounting to 162,572 kg (5.23 Moz) of gold, 201,015 kg (6.46 Moz) silver, 12,160 metric tons (t) of tin, and 28,088 t of copper. The lodes occur in veins, stockworks, breccia pipes, and replacement deposits that formed in epithermal to mesothermal temperature-pressure conditions. Fluid inclusion, isotopic age, mineral assemblage, alteration assemblage, and structural data indicate that many of the mineral deposits associated with Late Cretaceous-early tertiary volcanic and plutonic rocks represent geologically and spatially related, vertically zoned hydrothermal systems now exposed at several erosional levels. Polymetallic gold deposits of the Kuskokwim mineral belt are probably related to 77 to 52 Ma plutonism and volcanism associated with a period of rapid, north-directed subduction of the Kula plate. The geologic interpretation suggests that igneous complexes of the Kuskokwim mineral belt formed in an intracontinental back-arc setting during a period of extensional, wrench fault tectonics. The Kuskokwim mineral belt has many geologic and metallogenic features similar to other precious metal-bearing systems associated with arc-related igneous rocks such as the Late Cretaceous-early Tertiary Rocky Mountain alkalic province, the Jurassic Mount Milligan district of central British Columbia, the Andean orogen of South America, and the Okhotsk-Chukotka belt of northeast Asia.

Alaska↗

USGS1987

Age of uranium mineralization at the Jabiluka and Ranger deposits, Northern Territory, Australia: New U-Pb isotope evidence

The Ranger and Jabiluka uranium deposits are the largest in the Alligator Rivers uranium field, which contains at least 20 percent of the world's low-cost uranium reserves. Ore occurs in early Proterozoic metasediments, below an unconformity with sandstones of the 1.65-b.y.-old Kombolgie Formation. This study has used U-Pb isotope data from a large number of whole-rock drill core samples with a variety of mineral assemblages and textures. Ranger samples indicate a well-defined age of 1,737 + or - 20 m.y., consistent with earlier suggestions of the antiquity of this deposit. This age is distinctly pre-Kombolgie, so the Ranger deposit cannot have been formed by processes requiring its presence. The age is consistent, however, with mineralization related to heating associated with either the emplacement of early postmetamorphic granites, or possibly, with intrusion of the nearby Oenpelli Dolerite. In contrast, data for the least-altered Jabiluka ores yield a concordia intercept age of 1,437 + or - 40 m.y.--significantly younger than the Ranger age and also younger than the Kombolgie Formation. This age may correspond to a regional thermal event, as indicated both by mafic dikes of roughly this age and a zircon lower intercept age from a nearby granite-gneiss. Thus our data indicate that there must be at least three distinct periods of major U mineralization in the Alligator Rivers uranium field (including the previously determined approximately 900-m.y. age of the Nabarlek deposit), despite the fact that all of the deposits share strong similarities in their host rock, mineralogy, alteration, and geologic setting.Both Ranger and Jabiluka reflect a common, profound isotopic disturbance at about 400 to 600 m.y. This disturbance, which was especially pronounced at Jabiluka, may correspond to the development of basins and associated basalt flows to the west and southwest, as suggested by Crick et al. (1980).

Economic Geology↗

USGS1960

Deposits of the manganese oxides

One of the problems of the wartime program of studies of domestic manganese deposits concerned the identification of, and modes of origin of the manganese oxide minerals. Of the hundreds of specimens of the oxides collected in the United States, the minerals of about 250 specimens were identified by X-ray analysis; complete chemical analyses were made of about 35 specimens and partial analyses of about 150 specimens. This report presents the conclusions that arise out of a review of the geologic environment under which the specimens were found. One conclusion of this review concerns the supergene vs. hypogene origin of the oxides. In order to reach conclusions concerning the supergene and hypogene origin of the 33 oxides of manganese recognized thus far, it was necessary to define the criteria that seemed usable.One group of oxides appears to be persistently supergene: groutite, hydrohausmannite, lithiophorite, rancieite, hetaerolite, hydrohetaerolite, chalcophanite, crednerite, woodruffite, and wad. Another group of oxides appears to have been formed only by hypogene processes: manganosite, hausmannite, pyrochroite, bixbyite, galaxite, jacobsite, franklinite, pyrophanite, and ilmenite. A third group of oxides appear to have been formed by supergene processes in some places and by hypogene processes in other places: manganite, pyrolusite, ramsdellite, cryptomelane, psilomelane, hollandite, braunite, and coronadite.Another conclusion concerns a genetic relation between: (1) veins of manganese oxides in the southwest, largely in Tertiary volcanic rocks, (2) bodies of oxides in travertine aprons near active hot springs, and inactive Pleistocene springs, and (3) stratified oxides, largely in late Tertiary sedimentary rocks in the southwest. From the features of these three groups of deposits of oxides and their geologic and geographic distribution, it appears that hot water from great depth rose on fractures in areas of volcanic activity, deposited oxides in the fractures, appeared at the surface as hot springs, deposited oxides in the aprons near the springs and continuing to local basins, deposited manganese oxides with local debris as persistent beds in sediments, partly or wholly of volcanic origin.

Economic Geology↗

USGS2016

Book review: Mineral resource estimation

Mineral Resource Estimation is about estimating mineral resources at the scale of an ore deposit and is not to be mistaken with mineral resource assessment, which is undertaken at a significantly broader scale, even if similar data and geospatial/geostatistical methods are used. The book describes geological, statistical, and geostatistical tools and methodologies used in resource estimation and modeling, and presents case studies for illustration. The target audience is the expert, which includes professional mining geologists and engineers, as well as graduate-level and advanced undergraduate students. Review info: Mineral Resource Estimation . By Mario E. Rossi, Clayton V. Deutsch . 2014 . ISBN 978-1-4020-5716-8 332 pp.

Economic Geology↗

USGS1985

The Schwartzwalder uranium deposit. I: Geology and structural controls on mineralization.

Numerous uranium veins occupy fractures and faults in brittle Proterozoic gneisses along the east central Front Range of Colorado. The deposit size correlates with the density and localization of brittle fracture. The largest deposit, the Schwartzwalder, is explained by a singular configuration of complexly broken, deep-reaching brittle gneisses between impervious schists. The gneisses are described as being derived from volcanic rocks, shales, and chemical sediments, including iron, quartz and sulphide formations.-G.J.N.

Economic Geology↗

USGS1950

Characteristics of marine uranium-bearing sedimentary rocks

Many marine sedimentary black shale and phosphorite formations contain 0.01 to 0.02 percent uranium, and one, the alum shale of Sweden, contains as much as 0.5 percent. The published fact that uranium is already being recovered on a laboratory scale from Swedish deposits forcefully suggests that similar deposits in the United States and possibly many other countries may prove to be an important future source of uranium.The marine uranium-bearing black shales are rich in organic matter and sulfides and contain little or no carbonate. The best are found in relatively thin formations of pre-Mesozoic age. The nature of the uranium-bearing mineral or compound is not known. In contrast, nonmarine black shales, as a group, are not uraniferous.All marine phosphorites tested thus far are uraniferous and so too are the phosphatic nodules found in many marine black shales. With some exceptions, the uranium increases in a general way with increase in phosphate content and is believed to be in the phosphate mineral. Like the black shales, the phosphorite formations are characteristically thin; many are associated with unconformities or, in other words, periods during which little else in the way of sediment accumulated.Significant concentrations of uranium in marine sediments other than black shales and phosphorites are thus far known only in beach placer deposits and the gold-bearing conglomerates of the Witwatersrand district, South Africa.Uranium may be found in other types of marine sediments on further prospecting, but especially promising are the sediments rich in organic matter, phosphate, or both, found in relatively thin formations believed to be the entire depositional products of long periods of geologic time. Such formations are most characteristic of those areas where, at the time of deposition, the adjacent land masses were so stable and low that the influx of clastic materials was small; the basin of deposition was large or of such configuration that fine-grained sediments could accumulate; and chemical conditions in the seawater prevented deposition of large amounts of carbonate.

Economic Geology↗

USGS1993

Distribution of fluoride in ground water of West Virginia

This report describes the results of a study by the U.S. Geological Survey, in cooperation with the West Virginia Geological and Economic Survey, to evaluate the distribution of fluoride in ground water of West Virginia. Fluoride is a natural chemical constituent in domestic and public water supplies in West Virginia. Fluoride concentrations of about 1.0 milligram per liter in drinking water are beneficial to dental health. Concentrations greater than 2.0 milligrams per liter, however, could harm teeth and bones. Fluoride concentra- tions in ground water of West Virginia range from less than 0.1 to 12 milligrams per liter. Fluoride concentrations that exceed 2.0 milligrams per liter are found in wells drilled to all depths, wells drilled in all topographic settings, and wells drilled into most geologic units. Most fluoride concentrations that exceed 2.0 milligrams per liter are located at sites clustered in the northwestern part of the State.

Open-File Report↗

USGS1957

Effects of radon in drill holes on gamma-ray logs

Drill holes in uranium deposits in the Todilto limestone of Late Jurassic age near Grants, New Mexico, do not yield duplicate gamma-ray logs when probed at different times; some logs show equivalent uranium greatly in excess, in thickness and grade, of the chemical and laboratory radiometric analyses. Radon and its daughter products principally cause the discrepancies. Experimental work was undertaken by the writers to learn the relations of the radon to the uranium deposits and its behavior under different physical conditions. The work is based on the interpretation of about 600 gamma-ray logs, taken from 480 drill holes.Abnormally high amounts of radon, referred to here as contamination, ranged from barely detectable amounts to amounts that emitted as much radiation as ore-grade material. Most contaminated holes were in the higher-grade ore, and the contamination increased with elapsed time after drilling. Geologic conditions favorable for contamination by radon and its daughter products in drill holes are: proximity to uranium deposits and fractured or highly permeable rocks above the water table. Most drill holes can be decontaminated by blowing them out with compressed air or filling them with water. Water, however, tends to reduce the thickness-times-grade figures below the amounts determined in air.

New Mexico↗