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U.S. GEOLOGICAL SURVEY OPEN-FILE REPORT 2004-1372

Whole Rock Geochemical Data For Altered And Mineralized Rocks, Red Dog Zn-Pb-Ag District, Western Brooks Range, Alaska

John F. Slack,1 Karen D. Kelley,2 and Jeffrey L. Clark3


1 U.S. Geological Survey, National Center, MS 954, Reston, VA 20192
2U.S. Geological Survey, Denver Federal Center, MS 964, Denver, CO 80225
3Teck Cominco American Limited, 15918 E. Euclid Avenue, Spokane, WA 99216

INTRODUCTION

This report presents geochemical analyses for 220 mostly altered and mineralized rock samples from the Red Dog Zn-Pb-Ag district in the western Brooks Range of northern Alaska. These data form the basis for a study by Slack et al. (2004a) on hydrothermal silicification and related alteration in wall rocks of the Red Dog deposits and the Anarraaq deposit 10 km to the northwest. The sulfide deposits occur within the Ikalukrok unit (informal name) of the Mississippian Kuna Formation (Moore and others, 1986). Principal rock types that were analyzed include black and gray shale, unmineralized bedded barite, mineralized (sulfide-rich) bedded barite, sulfide-rich silica rock (replaced barite), massive and semimassive sulfide, vein chalcedony, and Brookian (Cretaceous) vein quartz. For stratigraphic completeness, data are also reported here for a limited number of unaltered and unmineralized samples of black and gray shale, laminated carbonate-rich shale, lithic turbidite, bedded siliceous rock, calcareous radiolarite, and tectonic mélange. Detailed descriptions of the sampled sulfide deposits and their stratigraphic settings are given in Slack and others (2004a) and Kelley and others (2004a, b). The geochemical analyses are presented here in Microsoft Excel and .dbf (included in .zip file) formats in order to facilitate calculations and plotting of data. A related geochemical database on unaltered Paleozoic sedimentary rocks of the western Brooks Range is available in Slack and others (2004b).

SAMPLE DESCRIPTIONS

Brief descriptions of the samples are included in the spreadsheets. Massive sulfide contains more than 50 volume percent sulfide minerals, whereas semimassive sulfide contains ~30-50 volume percent. Note that pyrite may include marcasite in some occurrences, especially those within laminae, veins, and in semimassive to massive sulfide.

SAMPLE PREPARATION

Geochemical analyses were obtained mostly on samples of diamond drill core 3.5 or 4.5 cm in diameter. Several analyzed samples come from mine faces within the Red Dog open pit (Main deposit) or from outcrops in the region. Samples were cut using water-cooled diamond saws in order to remove oxidized and(or) weathered surfaces. Particular care was taken to cut out visible veins from altered wall rocks so that each analysis would represent a single rock type. Note, however, that disseminated and laminated sulfides (e.g., pyrite laminae in black shale) were retained in the samples prior to analysis. All samples were pulverized in an alumina ceramic mortar, which in some cases may have produced very minor contamination by trace amounts of Al, Ba, and(or) rare earth elements (REE).

ANALYTICAL METHODS

Prior to analysis all samples were fused with lithium metaborate/tetraborate to insure nearly complete acid digestion of resistate minerals such as zircon, monazite, rutile, chromite, and barite. All samples were analyzed by Activation Laboratories (ACT Labs) in Ancaster, Ontario, using methods described on their web site: http://www.actlabs.com/. Major elements, most trace elements, and REE were determined by inductively-coupled plasma mass spectrometry (ICP-MS), using an approach similar to that of Jenner and others (1990). REE in some barite samples were analyzed by high-resolution, magnetic sector ICP-MS using an ion exchange technique in order to eliminate Ba interference on Eu. Volatiles and related components (total C, CO2, Corg, S, SO4) were determined using conventional methods as described in Jackson and others (1987). Fluorine was analyzed by the ion selective electrode technique (Jackson and others, 1987). Data for Sc, Cr, Co, Au, Sb, As, and Se in most samples were obtained by instrumental neutron activation analysis (Hoffman, 1992), which provides more precise results than by ICP-MS. Au concentrations in most samples of semimassive and massive sulfide were also obtained by flame atomic absorption (Aruscavage and Crock, 1987) by XRAL Laboratories of Denver, CO, using on splits of the same rock powders that were earlier run for major and trace elements, and REE.

Multiple standards were analyzed together with the submitted rock samples. Analyses by ACT Labs included data on 8 to 10 compositionally different standards with well-defined elemental concentrations. In addition to these standards, analyses were routinely obtained on duplicate samples and Ohio black shale SDO-1 (http://minerals.cr.usgs.gov/geochem/ohioshale.html). Precision and accuracy for concentrations ≥100× the minimum detection limit (MDL) was generally better than ±5 percent relative, and in many cases such as for major elements was better than ±1 percent relative. For concentrations approximately 10× the MDL, precision and accuracy were about ±10–20 percent relative depending on the method used.

DATA PRESENTATION

Data for elements, oxides, and other components are presented either in weight percent or parts per million, except for Au that are in parts per billion. Qualified values (shown by the “<” symbol) represent values less than the specified MDL. In some cases, the MDL for a particular element or component is not uniform, which reflects changing analytical conditions or matrix effects, or use of newer ICP-MS instruments that have higher precision and lower MDLs. For statistical treatment of data and other calculations, it is recommended that qualified values be substituted by one-half the analytical detection limit (Sanford and others, 1993). Note that the abbreviation “n.a.” refers to a lack of analysis for the specified element or component.

Values for the magnitude of the Ce and Eu anomalies are also presented. The magnitude of the Ce anomaly, Ce/Ce*, is calculated as: CeCN/((LaCN)0.667*(NdCN)0.333) where CN represents normalization of Ce, La, and Nd to average chondrites using the data of Nakamura (1974). The magnitude of the Eu anomaly, Eu/Eu*, is calculated as: EuCN/(SmCN*GdCN)0.5 with chondrite normalization of Eu, Sm, and Gd.

REFERENCES CITED

Aruscavage, P.J., and Crock, J.G., 1987, Atomic absorption methods: U.S. Geological Survey Bulletin 1770, p. C1–C6.

Hoffman, E.L., 1992, Instrumental neutron activation in geoanalysis: Journal of Geochemical Exploration, v. 44, p. 297–319.

Jackson, L.L., Brown, F.W., and Neil, S.T., 1987, Major and minor elements requiring individual determination, classical whole rock analysis, and rapid rock analysis: U.S. Geological Survey Bulletin 1770, p. G1–G23.

Jenner, G.A., Longerich, H.P., Jackson, S.E., and Fryer, B.J., 1990, ICP-MS: A powerful tool for high-precision trace-element analysis in earth sciences: Evidence from analysis of selected U.S.G.S. reference samples: Chemical Geology, v. 83, p. 133–148.

Kelley, K.D., Dumoulin, J.A., and Jennings, S., 2004a, The Anarraaq Zn-Pb-Ag and barite deposit, northern Alaska: Evidence for replacement of carbonate by barite and sulfides: Economic Geology, v. 99 (in press).

Kelley, K.D., Leach, D.L., Johnson, C.A., Clark, J.L., Fayek, M., Slack, J.F., Anderson, V.M., Ayuso, R.A., and Ridley, W.I., 2004b, Textural, compositional, and sulfur isotope variations of sulfide minerals in the Red Dog Zn-Pb-Ag deposits, Brooks Range, Alaska, USA: Implications for ore formation: Economic Geology, v. 99 (in press).

Moore, D.W., Young, L.E., Modene, J.S., and Plahuta, J.T., 1986, Geologic setting and genesis of the Red Dog zinc-lead-silver deposit, western Brooks Range, Alaska: Economic Geology, v. 81, p. 1696–1727.

Nakamura, N., 1974, Determination of REE, Ba, Fe, Mg, Na, and K in carbonaceous and ordinary chondrites: Geochimica et Cosmochimica Acta, v. 38, p. 757–775.

Sanford, R.F., Pierson, C.T., and Crovelli, R.A., 1993, An objective replacement method for censored geochemical data: Mathematical Geology, v. 25, p. 59–80.

Slack, J.F., Kelley, K.D., Anderson, V.M., Clark, J.L., and Ayuso, R.A., 2004a, Multistage hydrothermal silicification and Fe-Tl-As-Sb-Ge-REE enrichment in the Red Dog Zn-Pb-Ag district, northern Alaska: Geochemistry, origin, and exploration applications: Economic Geology, v. 99 (in press).

Slack, J.F., Schmidt, J.M., and Dumoulin, J.A., 2004b, Whole rock geochemical data for Paleozoic sedimentary rocks of the western Brooks Range, Alaska: U.S. Geological Survey Open-File Report 2004–1371.



U.S. Department of the Interior, U.S. Geological Survey
URL: http://pubs.usgs.gov/of/2004/1372/2004-1372.html
For more information, contact John F. Slack
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