OREAS 277b

OREAS 277b was prepared from a blend of high grade gold-bearing ore and barren sediments (shale, quartz and limestone). The ore was sourced from the Leeville Mine, located near the western crest of the Tuscarora Mountains, about 20 miles northwest of Carlin in Nevada, USA. Leeville is an underground high-grade refractory gold deposit located on the Carlin Trend. Gold mineralisation is hosted within decalcified and weakly to moderately silicified rocks composed of 60 to 70% quartz, 10 to 30% dolomite, 5 to 12% kaolinite, 2 to 4% illite and 2 to 4% pyrite (Jackson et al, 1997).
Carlin-style gold mineralisation is known to be ‘double-refractory’. The gold  particles are sub-microscopic and finely disseminated among a sulphide-rich matrix in the presence of carbonaceous material. Matching your standards to the matrix and mineralisation style of your field samples is very important, as a mismatch could result in low gold recovery.

OREAS 277b has been characterized for gold, majors and traces using the following methods:

• Gold by fire assay with AAS, ICP-OES or ICP-MS finish
• Full ICP-OES and ICP-MS elemental suites by 4-acid (HNO3-HF-HClO4-HCl) digestion
• Full ICP-OES and ICP-MS elemental suites by aqua regia digestion
• Total Carbon and Sulphur with infrared combustion analysis

Certified values for applicable analytes are operationally defined for each method, with results under OREAS ISO 17034 scope of accreditation.