U.S. GEOLOGICAL SURVEY OPEN-FILE REPORT 2004-1371
Whole Rock Geochemical Data For Paleozoic Sedimentary Rocks
of the Western Brooks Range, Alaska
John F. Slack,1 Jeanine M. Schmidt,2 and Julie A. Dumoulin2
1 U.S. Geological Survey, National Center, MS 954, Reston, VA 20192
2U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508
This report presents geochemical analyses for 210 unaltered and unmineralized rock samples of Paleozoic age in the western Brooks Range of northern Alaska. These data form the basis for a study by Slack and others (2004a) on the provenance and depositional history of the Paleozoic strata, and on their metallogenic significance relative to the formation of large stratabound Zn-Pb-Ag deposits in the Red Dog mining district. Principal rock types that were analyzed include shale, siltstone, sandstone, chert, bedded siliceous rock, and calcareous radiolarite; selected samples of limestone, phosphate, and argillite, and one siderite concretion, were also analyzed. Note that the phosphate samples are from the central Brooks Range, east of the Red Dog district. The geochemical analyses are presented here in Microsoft Excel™ and .dbf (part of .zip file) formats in order to facilitate calculations and plotting of data. A related geochemical database on altered and mineralized rocks in the Red Dog Zn-Pb-Ag district is available in Slack and others (2004b).
Brief lithologic descriptions of the samples are included in the spreadsheets.
All sample types are common rocks except for bedded siliceous rock and calcareous
radiolarite. The former lithology is a dark hard rock consisting mostly of
fine-grained quartz with minor iron sulfides and hematite, which Slack and
others (2004a) interpret as a mixed deposit of biogenic silica with an appreciable
eolian component. Calcareous radiolarite is a type of fine-grained limestone
composed mainly of radiolarians that have been replaced by calcite (Dumoulin
and others, 2004).
Geochemical analyses were obtained mostly on samples from natural outcrops; some
samples are of diamond drill core 3.5 or 4.5 cm in diameter. Samples were cut
using water-cooled diamond saws in order to remove oxidized and(or) weathered
surfaces. A small number of samples contain veins composed of quartz with or
without associated carbonate and sulfides; these veins were also cut out before
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).
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. Most samples were analyzed by Activation
Laboratories (ACT Labs) in Ancaster, Ontario, using methods described on their
web site: 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
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 (INAA) (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
were earlier run for major and trace elements, and REE.
A smaller group of samples was analyzed by the U.S. Geological Survey in
laboratories at Denver, Colorado, Reston, Virginia, and Menlo Park, California.
were determined by X-ray fluorescence using the methods of Taggart and others
(1987). Concentrations of volatiles and fluorine were determined by the same
procedures as outlined above, except that separate determinations of organic
carbon were not made. Where data for CO2 are available, organic carbon contents
were calculated by percent difference using results for total carbon. Minor
elements were analyzed by inductively coupled plasma-atomic emission spectometry
and others, 1987), except for Rb, Cs, Ba, Zr, Hf, Ta, Th, U, Sc, Cr, Co,
Ni, Mo, Zn, Au, Sb, and As and REE (La, Ce, Nd, Sm, Eu, Tb, Yb, Lu) that
by INAA (Baedecker and McKown, 1987).
Multiple standards were analyzed together with the submitted rock samples.
Analyses by ACT Labs included data on 8 to 10 compositionally different
well-defined elemental concentrations. In addition to these standards,
analyses were routinely obtained on duplicate samples and Ohio black shale
Precision and accuracy for concentrations ≥100× the minimum detection limit
(MDL) was generally better than ±5 percent relative, and in many cases such as
elements was better than ±1 percent relative. For concentrations approximately
10× the MDL, precision and accuracy were about ±10–20 percent relative depending
method used. Similar procedures were used for the analyses by the U.S.
Geological Survey, with comparable results for precision and accuracy.
Data for elements, oxides, and other components are presented either in weight
percent or parts per million, except for Au and Pt 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)
CN represents normalization of Ce, La, and Nd to average chondrites using the
data of Nakamura (1974). For the majority of samples for which ICP-MS data
are available for all REE, the magnitude of the Eu anomaly, Eu/Eu*, is
as: EuCN/(SmCN*GdCN)0.5 with chondrite normalization of Eu, Sm, and Gd. For
those samples without ICP-MS analyses for Gd, the Eu/Eu* values were calculated
a curve-fitting Excel™ macro program using INAA data for La, Ce, Nd, Sm, Eu,
Tb, Yb, and Lu.
Aruscavage, P.J., and Crock, J.G., 1987, Atomic absorption methods: U.S. Geological
Survey Bulletin 1770, p. C1–C6.
Baedecker, P.A., and McKown, D.M., 1987, Instrumental
neutron activation analysis of geochemical samples: U.S. Geological Survey
Bulletin 1770, p. H1–H14.
Dumoulin, J.A., Harris, A.G., Blome, C.D., and
Young, L.E., 2004, Depositional settings, correlation, and age of Carboniferous
rocks in the western Brooks
Range, Alaska: Economic Geology, v. 99 (in press).
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
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
Evidence from analysis of selected U.S.G.S. reference samples: Chemical
Geology, v. 83, p. 133–148.
Lichte, F.E., Golightly, D.W., and Lamothe,
P.J., 1987, Inductively coupled plasma-atomic emission spectrometry: U.S.
1770, p. B1–B10.
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:
Geology, v. 25, p. 59–80.
Slack, J.F., Dumoulin, J.A., Schmidt,
J.M., Young, L.E., and Rombach, C.S, 2004a, Paleozoic sedimentary rocks in
vicinity, western Brooks Range, Alaska: Provenance, deposition,
and metallogenic significance:
Economic Geology, v. 99 (in press).
Slack, J.F., Kelley,
K.D., and Clark, J.L., 2004b, Whole rock geochemical data for altered and
Range, Alaska: U.S. Geological Survey Open-File Report
Taggart, J.E., Jr., Lindsay, J.R., Scott, B.A., Vivit,
D.V., Bartel, A.J., and Stewart, K.C., 1987, Analysis
wavelength-dispersive X-ray fluorescence spectrometry:
U.S. Geological Survey Bulletin 1770,
U.S. Department of the Interior, U.S. Geological Survey
For more information, contact John F. Slack
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