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David Carl Hedlund

Publications and source records attributed to David Carl Hedlund.

16 recordsLinked to original sources
USGS1979

Background information to accompany folio of geologic, mineral resource, geochemical, aeromagnetic, and gravity maps of the Hillsboro and San Lorenzo quadrangles, Sierra and Grant Counties, New Mexico, with sections on geochemistry and geophysics

The Hillsboro and San Lorenzo 15-minute quadrangles of southwestern New Mexico have been mapped at a 1:48,000 scale and selected mineralized areas within these quadrangles have been mapped in greater detail. This area of about 550 mi2 (1,424 km2) is within the southern part of the Black Range and includes much of the Mimbres Mountains and parts of the adjoining Black Range Primitive area. The region is highly mineralized with Laramide (75.1 ? 2.5 m.y.) and middle Tertiary (about 32 to 35 m.y.) intrusions providing the source for much of the base- and precious-metal mineralization. The porphyry copper deposit at Copper Flat is a subvolcanic Laramide quartz monzonite stock that was intruded into a thick section (>2,700 ft or >823 m) of Upper Cretaceous andesite. Numerous gold-bearing veins radiate from the central quartz monzonite stock, and locally offset a radial system of quartz latite dikes. Gold-bearing veins, chiefly along the south and east periphery of the stock, have provided the source for both gold lode and placer deposits. The middle Tertiary rhyolitic plugs, stocks, and dikes have intruded a dominantly carbonate section of Paleozoic sediments and bedding replacement deposits of zinc, lead, and copper are closely associated with tactite in the Carpenter (Swartz) mining district. The rich oxidized silver deposits of the Kingston district are largely fault controlled and a metallizing pluton is not present at the surface outcrop. Some of the silver-bearing base-metal veins in the Kingston district contain rhodochrosite, rhodonite, and alabandite and the highly oxidized parts of these veins have been mined for manganese ore. Very minor amounts of tungsten, as scheelite, occur in thin tactite zones along Tank Canyon, at the Silver Queen claims near Kingston, and at the Silver Tail group of mines along Pierce Canyon.

New Mexico↗
USGS1974

Stratiform chromitite at Campo Formoso, Bahia, Brazil

Serpentinized ultramafic rocks of pre-Minas age (Precambrian) crop out in an elongate belt 1 km wide and 15 km long on the west side of the Serra de Jacobina near Campo Formoso, Brazil. The original stratiform ultramafic body has been so metamorphosed, faulted, and eroded that only narrow dismembered segments occur along the thrust-faulted west side of the Serra de Jacobina. The most economically important segment is that near Campo Formoso where chromitite layers can be followed for about 8 km near the base of the intrusion. Three to five chromitite layers of minable thicknesses have been mapped, the thickest being 1.4 to 1.8 m. The aggregate thickness of chromitite is about 5 m and the average grade is about 43.5 percent Cr 2 0 3 . The Cr:Fe ratio ranges from 1.6:1 in weathered friable chromite to 3:1 in massive unweathered chromitite; in cleaned chromite concentrates the ratio is as much as 3.3:1. Estimates of indicated chromite ore reserves range from 16 to 20 million metric tons, of which only an estimated 6 million tons can profitably be mined. Factors preventing full exploitation of the chromite include (1) the local presence of as much as 7 m of overlying colluvium, (2) the extremely faulted character of the chromitite layers, (3) the presence of an overlying quartzite thrust plate very near the line of chromitite outcrops, and (4) the steep dips of the chromitite layers, 15° to 40° along the Pedrinhas-Limoeiro trends and 50° to 65° along the Cascabulhos trend.

Bahia↗