Microanalytical trace element techniques (such as ion probe or laser ablation ICP‐MS) are hampered by a lack of well characterized, homogeneous standards. Two silicate glass reference materials produced by National Institute of Standards and Technology (NIST), NIST SRM 610 and NIST SRM 612, have been shown to be homogeneous and are spiked with up to sixty one trace elements at nominal concentrations of 500 μg g‐1 and 50 μg g‐1 respectively. These samples (supplied as 3 mm wafers) are equivalent to NIST SRM 611 and NIST SRM 613 respectively (which are supplied as 1 mm wafers) and are becoming more widely used as potential microanalytical reference materials. NIST however, only certifies up to eight elements in these glasses. Here we have compiled concentration data from approximately sixty published works for both glasses, and have produced new analyses from our laboratories. Compilations are presented for the matrix composition of these glasses and for fifty eight trace elements. The trace element data includes all available new and published data, and summaries present the overall average and standard deviation, the range, median, geometric mean and a preferred average (which excludes all data outside ± one standard deviation of the overall average). For the elements which have been certified, there is a good agreement between the compiled averages and the NIST data. This compilation is designed to provide useful new working values for these reference materials.

No abstract

Three distinct tectonic regimes were identified for felsic and intermediate volcanic rocks using published datasets from twenty-six different geographical locations around the world. The three well-defined tectonic regimes include oceanic arcs, active continental margins and within-plate volcanic zones. This subdivision is based on concentrations and ratios of the incompatible trace elements Ta, Th and Yb as geochemical tectonic discriminants. The separation of tectonic regimes is demonstrated on two discriminant diagrams, where the three zones are separated by ca. 45° diagonal lines on one, and by horizontal lines on the other. The ca. 45° trends of the boundaries between tectonic provinces on a Ta/Yb versus Th/Yb diagram are due to the similar incompatibility of Th and Ta relative to the somewhat lower incompatibility of Yb. On a Th/Ta versus Yb diagram, the three tectonic zones are separated by horizontal lines; datasets within individual zones have characteristic Th/Ta values, ca. 1-6 for within-plate volcanic zones, >6-20 for active continental margins, and >20-90 for oceanic arcs. These discriminant diagrams can be successfully used to identify the tectonic environments of intermediate and felsic volcanic rocks , and to evaluate the tectonic history of a region.

Archaean felsic metavolcanic rocks in the Superior Province of the Canadian Shield may be divided into three major groups on the basis of trace-element abundances and ratios. (1) FI felsic metavolcanic rocks are dacites and rhyodacites characterized by steep REE patterns with weakly negative to moderately positive Eu anomalies, high Zr/Y, low abundances of high-field-strength elements (e.g., HREE, Y, Zr, Hf), and high abundances of Sr. Examples occur in the Bowman Subgroup and Skead Group in the Abitibi Belt, in the Kakagi Lake, Lake of the Woods, Shoal Lake, and Sturgeon Lake areas of the Wabigoon Belt, and in the Confederation Lake area of the Uchi Belt. None of these horizons, as known, hosts base-metal sulphide deposits. (2) FII felsic metavolcanic rocks are rhyodacites and rhyolites characterized by gently sloping REE patterns with variable Eu anomalies, moderate Zr/Y, and intermediate abundances of HFS elements and Sr. Examples occur in the Misema Subgroup of the Abitibi Belt, in the Wabigoon Lake and Sturgeon Lake areas of the Wabigoon Belt, and in the Confederation Lake area of the Uchi Belt. Of these horizons, only those in the Sturgeon Lake area host base-metal sulphide deposits, and they exhibit the most pronounced negative Eu anomalies of this group. (3) FIII felsic metavolcanic rocks are rhyolites and high-silica rhyolites characterized by relatively flat REE patterns, which may be subdivided into two types. FIIIa felsic metavolcanic rocks exhibit variable negative Eu anomalies, low Zr/Y, and intermediate abundances of HFS elements and Sr. Examples occur in the Noranda mining district of the Abitibi Belt. FIIIb felsic metavolcanic rocks exhibit pronounced negative Eu anomalies, low Zr/Y, high abundances of HFS elements, and low abundances of Sr. Examples occur in the Kamiskotia, Kidd Creek, Matagami, and Noranda mining districts, the Garrison Subgroup in the Abitibi Belt, and at the South Bay mine in the Confederation Lake area of the Uchi Belt. All of these FIII horizons, with the exception of Garrison, host important base-metal sulphide deposits.These geochemical variations are interpreted to reflect differences in the petrogenesis of the felsic magmas, specifically, their formation or degree of modification in high-level magma chambers, which also influenced the formation of massive base-metal sulphide deposits. Most massive base-metal sulphide deposits in the Superior Province are underlain by subvolcanic magma chambers, which have been interpreted to have supplied heat to drive the ore-forming hydrothermal systems. FIII and some FII felsic volcanic rocks are interpreted to have been derived from these high-level magma chambers, accounting for their distinctive geochemical signatures and their association with massive base-metal sulphide mineralization. In contrast, FI felsic volcanic rocks are interpreted to have been derived from a deeper source and are considered to have escaped significant high-level modification, accounting for their distinctive geochemical signatures and the lack of associated base-metal sulphide mineralization. With certain limitations, the geochemistry of felsic metavolcanic rocks therefore may be used as a guide to identify prospective horizons for massive base-metal sulphide exploration in the Superior Province.

No abstract