Perspective. Certified Ontario reference materials programme at the Geoscience Laboratories, Sudbury, Ontario, Canada

Abstract

The Ontario Geoscience Laboratories (hereafter referred to as the Geoscience Laboratories) have produced 30 in-house materials since 1970. This experience, the limited availability of international rock standards in volume, and the recent acquisition of specialized equipment (capable of homogenizing up to 1 t of sample), has led to the development of the Certified Ontario Reference Materials programme for the production of certified reference materials (CRMs). Given the geological diversity of Ontario, the decision was made to create two streams of reference materials. One is a suite of unaltered and altered volcanic rock reference materials that reflected the wide compositional range of Archean rocks of Ontario. Sample sites are clustered in the Abitibi Greenstone Belt which includes the Timmins and Kirkland Lake mining camps. This region also hosts some of the world's largest and most prolific mines of Au and Cu–Zn, smaller Ni deposits and one of the two international type-localities of komatiite. Advantages of such a choice are extensive. The rocks in this area have been studied by the Ontario Geological Survey (OGS) for 50 years and this expertise is readily available both in terms of appropriate chemistry and in sampling sites. Geologically, Archean volcanic rocks were typically extruded into a subaqueous environment and cooled quickly. This facilitates a high degree of homogeneity. There are a wide variety of compositions available, clear association with mineral deposits and thus the reference materials may also provide excellent baseline material for environmental studies. In the 1970s, the OGS devised internationally used major element classification criteria which divided Archean volcanic rocks into three major clans that have several subtypes (komatiitic clan has ultramafic and basaltic members; tholeiitic clan has Fe-, Mg-, basaltic, dacitic, andesitic, and rhyolitic members; and calc-alkalic clan has basaltic, andesitic, dacitic and rhyolitic members). These rock types typically show different styles of alteration near ore deposits (i.e., chloritization, sericitization, carbonatization). The Archean volcanic rock suite will be comprised of these unaltered and altered rock types. The other group will focus on materials that fill a specific geoanalytical need. Based on the information above and the capacity of the Geoscience Laboratories geostandards programme (5 CRMs per year), it is anticipated that several rock types will be prepared yearly. A calc-alkaline rhyolite and an ultramafic komatiite have now been collected and other sites have been identified. Collection has commenced. After the sample is bottled, the homogeneity will be tested in our laboratories using validated methods. This will provide a tentative composition and will be followed by round-robin determinations. The reference materials will be released in 100 and 500 g plastic bottles to both the geoanalytical community and the exploration industry to monitor precision and accuracy in commercial surveys.