"The once prosperous gold, silver, copper and lead mines of the Searchlight mining district, Nevada, are situated along the south and western margins of a large quartz monzonite body. This intrudes the Precambrian gneisses and younger lava flows. Associated mineral veins show an eccentric type of zoning around the intrusive.
Seven rock samples of the quartz monzonite representing different parts of the intrusive were analyzed petrographically and spectrographically. Modal analyses and various types of rock alteration were investigated petrographically. Spectrochemical analyses of the rock samples and their major minerals were carried out for certain trace elements. A semi-quantitative method was used without internal standards. A simple synthetic silicate base was utilized for the preparation of standards to obtain working curves. The total energy method of Slavin proved satisfactory for Cu, Pb, Ni, Co, Cr, Ga, Mn, Sr, Ti, V and Zr but too insensitive for Zn, Ag and Au content.
Minerals of the rock samples were first separated and purified by reduction in grain size, use of the Frantz Isodynamic Separator, and careful selection under the binocular microscope.
Spectrochemical analyses of the purified minerals show that unaltered minerals contain more Cu and Pb than the altered ones. From the modal analysis of the rocks and the Cu and Pb content of pure minerals, mathematical computation permitted prediction of the possible Cu and Pb content of the original unaltered rock.
Ferromagnesian minerals contain anomalously high concentrations of Cu, Pb, Ni, Co, Mn, and Cr. The light colored minerals are poor in these elements, but are high in Sr and Ga. Cu appears to have been released in the alteration of green minerals to chlorite. Quartz samples show significant amounts of Cu and Pb, but this appears to be surface adsorption phenomenon, and suggests Cu and Pb solutions acted on the quartz.
Compared to other compilations, the Searchlight intrusive is low in Ga, Cr, Mn and V, normal in Cu, Ni, Ti, and Zn, and high in Pb and Sr. Little difference exists in the bulk trace element content of the apophyses and main intrusive body. This may be due to small proportion of mafic minerals in the rock. Cu is in greater quantity in the early formed pyroxene than later formed biotite. It is also more abundant in earlier plagioclase than later orthoclase. The Pb content in magnetite increases towards the north, while Ni, V, Ti and Cr decrease.
Unaltered minerals in the southern part of the intrusive show a higher Cu content than fresh minerals in the north, but altered minerals in the south are more depleted in Cu. The altered rocks also show a maximum decrease in Pb content near the lead producers. The ratio or Pb to Cu in the unaltered rock compared to the altered rock is 2.73:1, interestingly close to the production ratio of 2.6:1 of Pb to Cu.
The zoning and the spectrochemical data suggest the Searchlight intrusive is truly "productive". The possibility of predicting a "productive" intrusive and "non-productive" intrusive by trace element analyses might be further substantiated or disproved by more detailed studies of a similar nature. Altered and unaltered minerals of selected intrusives and bulk analyses of the rocks for the trace elements sought should determine if these elements have been released or retained by the parent rock. The former could be a guide to a "productive" intrusive"--Abstract, pages ii-iv.
Proctor, Paul Dean, 1918-1999
Tappmeyer, Wilbur P.
Kennedy, Richard R. (Richard Ray)
Legsdin, Adolph, 1899-1969
Geosciences and Geological and Petroleum Engineering
M.S. in Geology
Missouri School of Mines and Metallurgy
ix, 94 pages
Clark County, Nevada
© 1961 Jai Nandan Shrivastava, All rights reserved.
Thesis - Open Access
Library of Congress Subject Headings
Soils -- Trace element content -- Nevada -- Clark County
Monzonite -- Nevada -- Clark County
Quartz -- Nevada -- Clark County
Geology -- Nevada -- Clark County
Geology, Stratigraphic -- Precambrian
Print OCLC #
Electronic OCLC #
Link to Catalog Record
Shrivastava, Jai Nandan, "Certain trace element distribution in the Searchlight, Nevada quartz monzonite, Clark County, Nevada" (1961). Masters Theses. 2782.