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://pubsdata.usgs.gov/pubs/of/2004/1372/2004-1372.html
For more information, contact John F. Slack
Maintained by Eastern Publications Group
Last modified: 23:38:30 Sat 12 Jan 2013
Privacy statement | General disclaimer | Accessibility