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P. K. Theobald

Publications and source records attributed to P. K. Theobald.

At least 37 records · Page 2Linked to original sources
USGS1981

Sequential extraction techniques applied to a porphyry copper deposit in the basin and range province

Samples of minus-80-mesh (<180 μm) stream sediment, rock containing exposed fracture coatings, and jarosite and chrysocolla were collected from an area surrounding the North Silver Bell porphyry Cu deposit near Tucson, Arizona. The samples were subjected to a series of extractions in a scheme originally designed for use on samples from humid or sub-humid environments, in which the following fractions can effectively be separated: (1) carbonates and exchangeable metals; (2) Mn oxides; (3) organic compounds and sulfides; (4) hydrous Fe oxides; and (5) residual crystalline minerals. Jarosite and chrysocolla, two major minerals of the North Silver Bell area, were found to dissolve over two or more steps of the extraction scheme. The results represent only a limited number of samples from one copper deposit. Nevertheless, they do suggest that in a semiarid to arid environment, where mechanical dispersion of such minerals predominates, uncritical assignment of unique phases, such as Mn oxides or organics to a given extraction would lead to false interpretations of weathering processes. However, the relative proportions of elements dissolved in each step of the jarosite and chrysocolla extractions could be used as a “fingerprint” for recognition of the presence of these two minerals in the stream-sediment and rock samples. The relative abundance of hydrous Fe oxide and jarosite and the alteration zoning could be mapped using data from jarosite and chrysocolla extractions. Manganese oxides were also found to have a greater influence on Zn than on Cu or Pb during supergene alteration. The rapid change in relative importance of the first (1 M -acetic acid) extraction for Cu, Zn, and Pb near the mineralized zone suggested the occurrence of minor hydromorphic processes within the stream sediments. Thus, the acetic acid extraction proved the most effective for pinpointing mineralization in sediments. In contrast, the residual fraction had the longest dispersion train, suggesting that total metal concentrations are most effective in arid environments for reconnaissance surveys.

Journal of Geochemical Exploration↗
USGS1980

Map showing the distribution of minerals in the heavy-mineral concentrate of stream sediments in the Sierra Ancha Wilderness and Salome Study Area, Gila County, Arizona

Reconnaissance geochemical and mineralogical sampling was done in the Sierra Ancha Wilderness and Salome Study Area during April and May 1978. This map shows the distribution of chalcopyrite, florite, galena, scheelite, and lead-rich iron oxides in the nonmagnetic fraction of the heavy-mineral concentrate of stream sediment samples collected during the reconnaissance study.

Arizona↗
USGS1971

Selected fluvial monazite deposits in the southeastern United States

Farther southwest in Georgia, around Griffin and Zebullon, along streams tributary to the Flint River in the monazite belt the flood plains are generally small and discontinuous, and only about 1 percent of the sediment is gravel. The area between Griffin, Zebullon, and the Flint River is underlain by biotite schist and biotite gneiss into which biotite granite has been intruded. Only along one stream, Flat Creek, which drains monazite-bearing granite near Zetella, Ga., are the tenors in monazite even moderately high, but a combination of thick, clayey overburden and discontinuous flood plains make the stream unsuitable for placer mining. Elsewhere in the Flint River area the heavy-mineral concentrates contain less than 1 percent monazite. The southwesternmost area in which reconnaissance of the monazite belt was conducted includes a groups of southwest-flowing tributaries to the Chattahoochee River north of Pine Mountain and near La Grange, Ga. A combination of three characteristics of the alluvium make the area unfavorable for mining: (1) the upper half of the sedimentary sequence is clay and silt, (2) there is scant gravel, and (3) much of the sand is fine grained. Monazite is associated with the Snelson Granite, schists, and gneisses north of the Towaliga fault, but even in this area the tenor of most riffle sediments is only 0.1 to 0.5 pound of monazite per cubic yard, and the average tenor of the alluvium is about 0.2 pound per cubic Yard. Rocks south of the Towaliga fault contain scant monazite. The monazite-bearing area in the drainage basin of the Chattahoochee River has no monazite placers. Evidence from the areas on the Flint and Chattahoochee Rivers shows that streams in western Georgia are a much poorer source of monazite than streams farther to the northeast in Georgia, South Carolina, and North Carolina. Also, the northeastern part of the belt in the drainage basins of the Yadkin and Dan Rivers is a poorer source for monazite than the area between the Savannah and Catawba Rivers, S.C.-N.C. Monazite-bearing crystalline rocks in the western belt contain about 0.06 pound of monazite per cubic yard. Residual soil derived from the crystalline rocks contains about 0.3 to 0.4 pound of monazite per cubic yard, and colluvial sediments formed by sheet-wash from saprolite, residual soil, and, rarely, old stream deposits, have an average of 3.1 pounds of monazite to the cubic yard. The data on the tenors of residual and colluvial deposits are far less comprehensive than those an the quantity of monazite in the crystalline rocks, but the tenors are probably of the correct order of magnitude. Neither the crystalline rocks nor the residual soils are ores of monazite. Because the colluvial deposits are thin and have patch distribution they could not be mined independently, but some colluvium could be stripped from the adjoining hills in conjunction with the mining of alluvial deposits in the valleys. It is most unlikely that alluvial monazite placers have formed in the trunk streams leading southeastward out of the monazite belt. Churn drilling on the Broad and North Tyger Rivers, South Carolina, at the east edge of the belt has shown that the bulk of the alluvium is fine-grained sediment that contains 0.2 to 0.4 pound of monazite per cubic yard--tenors that represent no considerable enrichment over those in the crystalline rocks and residual soils. The probable persistence of predominantly fine-grained alluvium downstream to the Coastal Plain and the certain dilution of monazite-bearing concentrates by the inflow of monazite-free suites of heavy minerals between the belt and the fall line suggest that the trunk streams east of the belt are the least favorable sources for alluvial monazite in the Piedmont?

Open-File Report↗
USGS1971

Geochemical maps of Samrah and vicinity, Kingdom of Saudi Arabia

Geochemical maps of Samrah and vicinity, near Ad Dawadimi, display anomalies for the ore metals over each of the major ancient mining sites, a large contamination anomaly over the ancient ore-processing waste, and less-well defined anomalies parallel to mineralized structures. Zirconium and lanthanum display negative anomalies over altered rocks, do not display the contamination anomaly, and, for zirconium, identify the west workings at Samrah as the site of most intense alteration.

Open-File Report↗
USGS1971

Al Kushaymiyah as a target for a Colorado-type molybdenite deposit

The granitic complex in the vicinity of Al Kushaymiyah was singled out by Whitlow (19,69, 1969a, 1971), as one of the most promising areas for exploration in the Southern Wajd quadrangle (Jackson and others, 1962). He noted in particular the intensity of shattering and silicification of these potassium-rich granites, and the presence of unusual concentrations of tungsten , molybdenum, and tin in samples from the area. In the light of shield-wide compilations, this area again stands out as the principal geochemical anomaly for the three metals. The similarity of these unusual geologic and geochemical features to those of Colorado-type molybdenite deposits is striking and suggests that the Al Kushaymiyah provides a favorableenvironment to explore for a stockwork molybdenum deposit.

Open-File Report↗
USGS1970

Geologic log and chemical data, diamond drill hole 1, Samrah, Kingdom of Saudi Arabia

Diamond drill hole number 1 at the Samrah ancient mine, Kingdom of Saudi Arabia penetrated a series of mineralized fractures. Lead, zinc, and silver are the principal ore metals and galena and sphalerito are the ore minerals identified to date. Throughout the core there is a somewhat better correlation of silver with zinc than with lead. The richest interval of core is in the main vein, 51-1/2 feet of core from 430 to 482 feet, and averages nearly 20 ounces of silver to the ton. Within this interval, 15 feet of core from 444 to 459 feet averages 60 ounces of silver to the ton. The richest single sample represents the five-foot interval from 454 to 459 feet and is reported to contain nearly 140 ounces of silver to the ton. All of these intervals contain recoverable quantities of lead and zinc and some contain a small amount of gold.

Open-File Report↗
USGS1962

Description, composition, and tenor of unconsolidated sediments in monazite-bearing tributaries to the Broad River in the western Piedmont of South Carolina and North Carolina

The accompanying 10 tables were prepared during 1953-54 to assist in the appraisal of fluviatile monazite placers in the basin of the Broad River, South Carolina and North Carolina. Principal results have been summarized (Overstreet, Theobald, and Whitlow, 19)9, p. 709- 714). Details of the exploratory drilling of four monazite placers in this area were released in 1953 and 1954 (Griffith and Overstreet, 1955a, p. 3-30; 1953b, p. 3-17; 1953c, p. 3-27; Hansen and Cuppels, 1954, p. 3-27). The samples described were panned by the writer, his co-workers, and assistants .etween July and November 1931 and April and November 19,2. Co-workers were J. W. Whitlow, W. C. Overstreet, A. M. White, N. P. Cuppels, and D. W. Caldwell. Assistants were J. W. Keeler in 19)1 and B. F. Spradlin, P. E. Myers, and J. W. Wissert, Jr., in 1952. The methods used to collect the samples and pan the concentrates have been described in detail (Theobald, 3.957, p. 3-6).

North Carolina, South Carolina↗