State of Alaska Alaska | Natural Resources DNR | Geological & Geophysical Surveys DGGS | Geochemistry Geochem

Sample Detail

Sample Number 15MBW025
Project Alaska strategic and critical minerals assessment project

Sample Documentation

Analyses [Download All]

Reference Number FA15152552,FA15152552/FA15181833
Reference Date 2015-11-01
Citation RDF 2015-17
Laboratory ALS Minerals
Laboratory Number 2015MBW25
Description Rock samples were collected for two different purposes. Samples of sulfide- or chromite-bearing rocks, or altered rocks, were preferentially collected and analyzed for trace-element geochemistry. Most samples are 'grab' samples, which were randomly collected at a location; however, a few samples are 'select' samples, which were deliberately collected from chromite-rich layers in ultramafic rocks. Igneous rocks showing little alteration or weathering were collected for whole-rock major-oxide, minor-oxide, and trace-element analyses to aid in classification and study of petrogenesis and tectonic setting. These igneous rocks were also analyzed for trace-element chemistry, as some of the samples contain sulfide(s) and (or) chromite. Rock samples were processed by ALS Minerals using their PREP-31 package. The samples were crushed to better than 70 percent passing 2 mm, and a 250 g split was pulverized to better than 85 percent passing 75 microns. Prior to crushing, samples for whole-rock analysis were trimmed by DGGS staff to remove weathering, and cut surfaces were sanded to remove any saw metal. Major- and trace-element compositions for rock samples were determined on a 1 g sample (ALS Minerals method ME-MS61) using a four-acid digestion followed by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and ICP-MS. Samples that exceeded detection limits for elements of interest were reanalyzed using specific elemental tests. For this report, samples with over-limit values for chromium (Cr) were reanalyzed using a 0.5 g split using four-acid digestion with ICP-AES (ALS Minerals procedure Cr-OG62). Platinum, palladium, and gold values were analyzed by 30 g fire assay with inductively coupled plasma-mass spectroscopy (ICP-MS) finish (ALS Minerals method PGM-MS23). Whole-rock geochemistry samples were analyzed using ALS Minerals complete whole-rock characterization package (CCP-PKG01) on a 10 g split. Major- and minor-oxide values were determined using lithium metaborate fusion digestion and ICP-AES (ALS Minerals method ME-ICP06). Relatively resistive trace elements, including rare-earth elements, were determined using a lithium borate fusion digestion and ICP-MS (ALS Minerals method ME-MS81); Ag, Cd, Co, Cu, Li, Mo, Ni, Pb, Sc, and Zn were determined by four-acid digestion and ICP-AES (ALS Minerals method ME-4ACD81); and As, Bi, Hg, Sb, Se, and Te were determined by aqua regia digestion followed by ICP-MS (ALS Minerals method ME-MS42). Total C and S were analyzed by Leco combustion furnace (ALS Minerals method ME-IR08).
Sample Type rock