Search USGS⌕ Search

Geology topics

George J. Neuerburg

Publications and source records attributed to George J. Neuerburg.

8 recordsLinked to original sources
USGS1978

The architecture of the porphyry-metal system as a prospecting stratagem in the Southern Rocky Mountains

A model of the porphyry-metal system characteristic of the consanguineous Cretaceous and Tertiary igneous rocks and associated ores of the southern Rocky Mountains is constructed from the bits and pieces exposed in the Colorado mineral belt and the San Juan volcanic field. Hydrothermally altered rocks in a part of the areas of mineralized rock associated with the Platoro caldera are matched against the model, to locate and to characterize latent mineral deposits for optimal prospecting and exploration. The latent deposits are two stockwork molybdenite deposits (porphyry-molybdenum) and one or two copper-gold-silver chimney deposits.

Open-File Report↗
USGS1978

A comparison of rock and soil samples for geochemical mapping of two porphyry-metal systems in Colorado

Paired rock and soil samples were collected at widely spaced locations in large segments of the porphyry-metal systems of the Montezuma district in central Colorado and of a northwestward extension of the Summitville district into Crater Creek in southern Colorado. The paired samples do not covary closely enough for one sample medium to proxy for the other. However, the areal distributions of elements in both rocks and soils in these two districts conform to alteration zoning as defined by mineralogy. Differing geochemical patterns of rocks and soils reflect species-dependent responses to weathering. Soils appear to be statistically enriched in ore elements and depleted in rock elements as compared to the matching rocks. These differences are largely artificial s owing to different methods of sample preparation and chemical analysis for rocks and for soils. The distributions of metals in soils delineate the occurrence of ore-metal minerals mostly from vein deposits whereas the distributions of metals in rocks conform to zones of pervasive hydrothermal alteration and to the distribution of varied mineral deposits among these zones. Rock and soil samples are equally useful s of comparable map resolution and complement one another as a basis for geochemically mapping these porphyry-metal systems.

Open-File Report↗
USGS1976

Ocher as a prospecting medium in the Montezuma district of central Colorado

Ocher occurs widely In the Montezuma district as small sinters and as bedded deposits of bog iron and ocher-cemented conglomerates. The iron of the ochers is derived from pyrite-rich veins and from pyritic hydrothermally altered rocks. Trace amounts of ore metals in the ocher and its admixed detritus are partly from the pyritic source rocks but also include contributions from other rocks and ores in the watershed, both during and after formation of the ocher deposit. Ocher is evidence for the presence and character of the generally ill exposed pyritic rocks, which are important, in evaluating the porphyry-metal system of ore deposits. The trace-element composition of the ocher is at best a qualitative guide to the ore metals present in the provenance of the ocher deposit but not to their abundance or necessarily to their mode of occurrence.

Colorado↗
USGS1975

Analysis for tellurium in rocks to 5 parts per billion

In the proposed method, a 12.5-g sample is digested with nitric acid and evaporated to dryness; the excess nitric acid is removed by reaction with formic acid. Tellurium is extracted from the dried residue into hydrobromic acid and is then coprecipitated with arsenic, using hypophosphorous acid as the reducing agent. The precipitate is dissolved in a solution of hydrobromic acid and bromine, from which the tellurium is extracted into 0.6 ml of methyl isobutyl ketone. Tellurium content is estimated by atomic absorption spectrophotometry. Recovery of tellurium from nitric acid solutions carried through the procedure approached 100 percent through the analytical range 5-200 ppb. The relative standard deviation of five consecutive analyses of USGS standard rock GSP-1 was 5.26 percent at a mean concentration of 20.8 ppb. Under optimum conditions an average of 20 samples may be analyzed per man-day.

Colorado↗
USGS1974

Molybdenite in the Montezuma District of central Colorado

The Montezuma mining district, in the Colorado mineral belt, is defined by an assemblage of porphyry, ore, and altered rocks that originated in the venting of a Tertiary batholith through weak structures in Precambrian rocks. The ore consists of silver-lead-zinc veins clustered on the propylitic fringe of a geometrically complex system of altered rocks, which is centered on the intersection of the Oligocene Montezuma stock with the Montezuma shear zone of Precambrian ancestry. Alteration chemistry conforms to the standard porphyry-metal model but is developed around several small intrusives strung out along the shear zone and is expressed as a mottled pattern, rather than as the usual thick concentric zones centered on one large plug. The distribution of trace amounts of molybdenite is consistent with the postulate of molybdenite deposits in the district, but the mottled alteration pattern may signify small and scattered, possibly very deep, deposits. Disseminated molybdenite is essentially coextensive with altered rock and increases slightly in quantity toward the inner alteration zones. Two groups of molybdenite veins, associated with phyllic and potassic alteration, represent possible diffuse halos of molybdenite deposits. One group of veins resembles the Climax and Henderson deposits but was seen only in a small and isolated area of outcrops. The second group of molybdenite veins is in a bismuth-rich part of the Montezuma stock and underlies an area of bismuth veins; this group records the passage of contact metasomatic ore fluids. Another bismuth-rich area is in the southeast corner of the stock in a region of bismuth veins and may indicate a third group of molybdenite veins.

Circular↗
USGS1973

Galkhaite, (Hg,Cu,Tl,Zn) (As,Sb)S2, from the Getchell mine, Humboldt County, Nevada

The first reported occurrence in the United States of galkhaite (Hg,Cu,Tl,Zn)(As,Sb)S 2 is at the Getchell mine, Humboldt County, Nev. The mineral occurs as brownish-black cubes associated with graphite, pyrite, and realgar. In polished section galkhaite is grayish white and isotropic with a deep-red internal reflection; reflectivity at 590 nm is 21.6 percent. Spectrographic analysis gave Hg 42 percent, Cu 5 percent, Zn 1.5 percent, Fe 0.7 percent, Tl 5 percent, As 24 percent, Sb 0.3 percent, and S (by difference) 21.3 percent. The mineral is cubic, a=10.36, and the strong lines of the X-ray powder pattern are 2.99 (100), 4.21 (90), 2.76 (80), 1.831 (70), 7.25 (60), 2.58 (40), 1.561 (40). The pattern is very similar to that of tetrahedrite except for the strong lines at 7.25, 4.21, and 2.76.

Nevada↗
USGS1956

Uranium content and leachability of some igneous rocks and their geochemical significance

The uranium content and its leachability in 442 igneous rocks if wide variety were measured. Four-gram samples, crushed below 38 mesh, were leached in in 0.05 M HNO 3 for half an hour at 80 to 85° C; the leachate and undissolved residue were analyzed fluorimetrically. This study explored the relation of uranium content and leachability to petrography. With few exceptions, the relations between uranium content, uranium leachability, rock leachability, rock type, and mineral composition seem to be random. Uranium content and leachability in homogeneous outcrops vary erratically, in heterogeneous outcrops the variation appears nonsystematic. Correlations with geologic environment indicate that uranium content and leachability are largely controlled by geologic processes during and after crystallization.

Trace Elements Investigations↗