Semiquantitative spectrographic analysis of drill core from Sunbeam mine, Custer County,Idaho


Semiquantitative spectrographic analysis of drill core from Sunbeam mine, Custer County,Idaho Geologists for Azcon Corporation, Salt Lake City, Utah undertook an exploratory drilling program at Sunbeam mine, Custer County, Idaho (figure 1) in the summer of 1976. Core from three drill holes (table 1) was made available to the U.S. Geological Survey by Sunbeam Mining Corporation in 1981 and was analyzed by Semiquantitative spectrographic methods in 1982. This report presents the results of those analyses. 
Sunbeam mine exploits a vein and disseminated gold-silver deposit hosted in rhyolite and pyroclastic rocks of Eocene age. The rhyolite intrudes volcaniclastic rocks of the Custer graben, one of several northeast-trending volcanotectonic features that form the trans-Challis fault system (Kiilsgaard and others, 1986). Brecciation and intense silicification followed intrusion of the rhyolite and affected both the rhyolite and the host rocks. Both the rhyolite and the adjacent pyroclastic rocks are altered to clay minerals and quartz. Zircon from altered rhyolite yielded a fission-track age of 45.8 _+ 2.3 Ma (Johnson and Mclntyre, 1983); this is thought to be the age of alteration and mineralization. The geologic relations (Mclntyre and Johnson, 1983) indicate that a closely contemporaneous interplay between intrusion, continued fracturing, and prolonged fracture-controlled circulation of hydrothermal fluids produced the observed patterns of alteration and mineralization. 
Sunbeam mine was first staked in 1879 but had was little production until a mill was erected in 1903. Litigation closed the mine in 1911 and it remained closed until modern exploration began in 1967. U.S. Bureau of Mines records indicate that total production was more than 18,000 oz gold and more than 23,000 oz silver (Johnson and Fisher, 1987). Early production was from fracture-controlled chimney-like veins in both rhyolite and pyroclastic rocks. Recent exploration has focused on disseminated metals around those veins. 
Table 2 shows the results of Semiquantitative spectrographic analysis of samples taken at approximately ten-foot intervals down the three 500-foot cores. Sample numbers show both the hole number and the number of feet from the surface. SB32056 is from hole number 32 at a depth of 56 ft. Spectrographic analysis was done by techniques described by Grimes and Marranzino (1968). Results were obtained by visual comparison of spectra derived from the sample against spectra obtained from standards made from pure oxides and carbonates. The values are reported by giving the nearest midpoint on a six-step scale using 1, 1.5, 2, 3, 5, 7, 10 .... as the midpoints of the intervals. Motooka and Grimes (1976) report that the precision of this method is approximately plus or minus one reporting interval at the 83 percent confidence level and plus or minus two intervals at the 95 percent confidence level. Sunbeam Drill Core Data Spec--continued 
3 2 2 2 2 5 5 3 3 3 5 5 3 2 3 3 3 3 3 3 3 3 3 3 3 3 2 3 3 3 3 3 3 3 3 3 3 3 3 3 5 3 3 3 5 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N 5 <0 <0 5 <0 <0 <0 <0 5 5 <0 <0 <0 5 <0 <0 5 
SB32010 SB32015 SB32026 SB32037 SB32040 SB32056 SB32065 SB32079 SB32085 SB32091 SB32102 SB32110 SB32120 SB32128 SB32137 SB32U5 SB32155 SB32168 SB32175 SB32184 SB32197 SB32207 SB32213 SB32224 SB32230 SB32239 SB32250 SB32259 SB32267 SB32276 SB32286 SB32297 SB32307 SB32313 SB32323 SB32340 SB32352 SB32361 SB32372 SB32381 SB32333 SB32400 SB32410 SB32415 SB32425 Mo Nb Ni Pb Sb Sc Sr Zn Zr N N N N N N N N N N N N N N N N N N N N N N 20 10 7 M N N N N N N 10 5 5 20 N <0 N <0 <0 N N N N <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 20 <0 <0 20 20 20 20 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 N N N N N N N N N N N N N N N N N N N N N 100 100 <0 N <0 N <0 <0 N N N <0 <0 <0 N N N N N N N N N <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <n <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 20 10 10 15 <0 <0 <0 <0 <0 <0 N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0
N N N N <0 N N N N N N N N N N N N N N N N N N N <0 <0 N N N N N N <0 N <0 N N N N N N 20 
3 3 5 3 3 3 3 2 2 3 3 3 3 3 3 3 3 2 2 2 2 2 2 3 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N 5 <0 <0 5 <0 <0 <0 <0 <0 5 
Sample SB32435 SB32445 SB32455 SB32462 SB32482 SB32490 SB32497 SB33015 SB33023 SB33035 SB33041 SB33050 SB33060 SB33070 SB33080 SB33087 SB33095 SB33105 SB33115 SB33120 SB33135 SB33UO SB33150 SB33160 SB33170 SB33174 SB33185 SB33195 SB33203 SB33211 SB33221 SB3323? SB33240 SB33248 SB332S6 SB33266 SB33276 SB3328S SB33292 SB33303 SB33311 SB33320 SB33327 SB33335 SB33345 Mo Nb Ni Pb Sb Sc Sr Zn N <0 10 10 N N N N N N N N N N N 10 N <0 N N N N N N N N N N N N N N N N N 1 5 5 10 1 5 1 5 <0 <0 <0 <0 <0 <0 <0 20 20 <0 <0 <0 <0 <0 <0 <0 20 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <n <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0
N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N <0 <0 5 5 <0 <0 5 <n 5 5 <0 <0 <0 5 5 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 10 <0 <0 <0 <0 <0 <0 <0 <0 N <0 N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N 10 
N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N
N N N N N N N N N N N N N N N N N N 500 N N N 500 500 <0 N N N N N N N N <0 500 <0 N N
<0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 <0 N N N N N N N N N N N N N 10 N <0 <0 N N N N N N M N 10 N N <0 N <0 N N N N N N 200 N <0 <0 <0 <0 <0 

Figure 1 .

 1 Figure 1. Index map for Sunbeam mine area, Custer County, Idaho, 


Table 1 .

 1 Location, orientation, and depth data for drill holes, Sunbeam mine 


	Hole	Collar	Latitude	Longitude	Bearing	Plunge	Total
	Number	Elev.					Depth
	32	7500'	44°26'06"	114°44'03.5"	N33°W	60°	500'
	33	7755'	44°26'08"	114°43'58.5"	N36°W	45°	500'
	34	7998'	44°26'07"	114°44'10"	N32°W	45°	500'

Table 2 .

 2 Geochemical data from drill holes, Sunbeam mine, Idaho. 


	Analyses by semiquantitative spectrographic methods. Values in parts per
	million unless otherwise noted. N = not detected at limit of detection.
	Analyses for the following elements yielded no values above the detection
	limits shown: Au (10), Bi (10), Cd (20), Sn (10), Th (100). Analyst:
	E.F. Cooley

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature, U.S. Geological Survey Denver, Colorado 80225 REFERENCES CITED Grimes, D. J., and Marranzino, A. P., 1968, Direct-current arc and alternatingcurrent spark emission spectrographic field methods for the semiquantitative analysis of geologic materials: U.S. Geological Survey Circular 591, 6 p. Johnson, K. M., and Fisher, F. S., 1987, High-level rhyolite-hosted preciousmetal deposits, j_n_ Fisher, F. S., and Johnson, K. M., eds., Preliminary manuscript for "Mineral-resource potential and geology of the Challis I°x2° quadrangle, Idaho": U.S. Geological Survey Open-File Report 87-480, p. 163-166. Johnson, K. M., and Mclntyre, D. H., 1983, Disseminated gold-silver deposit in a rhyolite dome at the Sunbeam mine, Custer County, Idaho [abs.]: Geological Society of America Abstracts with Programs, v. 15, no. 5, p. 324-325. Kiilsgaard, T. H., Fisher, F. S., and Bennett, E. H., 1986, The trans-Challis fault system and associated precious-metal deposits: Economic Geology, v. 81, p. 721-724. Mclntyre, D. H., and Johnson, K. M., 1983, Geologic map of part of the Sunbeam mine area, Custer County, Idaho: U.S. Geological Survey Open-File Report 83-329, 1 sheet, scale 1:2,400.
Kathleen M Johnson
Semiquantitative spectrographic analysis of drill core from Sunbeam mine, Custer County,Idaho