Regional reconnaissance exploration rock geochemistry for massive sulphides, New Brunswick, Canada

In the Bathurst District of New Brunswick there are more than 50 known occurrences of base metal sulphide mineralization within an area of Palaeozoic volcanic-sedimentary rocks approximately bounded by the Rocky Turn deposit in the north, the Key Anacon deposit in the east, the Heath Steele deposit in the south, and the Devil's Elbow deposit in the west. Only four of these occurrences are, or have been, producing mines; 19 are classed as “major occurrences”. The area is highly prospective for massive sulphide deposits of the Brunswick Mining and Smelting and Heath Steele type; it would obviously be of considerable importance to define the zones within the sequence where major occurrences should be sought.To determine whether exploration rock geochemistry could be used on a regional reconnaissance scale, 419 samples of rhyolite from an area of 2000 km² (at an average density of one sample per 5 km²) were analyzed for total content of Cu, Pb, Zn, Ca, Mg, K, Na, Fe, and Mn. The data were processed by calculating the geometric mean of all samples in cells of approximately 10 km². Contrary to the relations documented on a mine scale (within one kilometre of major deposits), where the clearest halos are given by major elements, it is the ore elements that give the best regional patterns.The producing mines and the most important of the known occurrences all lie in zones where rhyolite contains less than 10 ppm Cu. Element ratios considerably enhance anomalous relations. The Zn:Pb ratio of the sulphides in the main deposits is 2.4–2.8, regardless of grade. It is demonstrated that all present and past producing mines and the most important known major occurrences lie within well-defined zones of Zn:Pb ratios of 2.4–2.8. Similarly, zones where the Pb:Cu ratio is > 3.0 and the Zn:Cu ratio is > 7.0 also define the most important deposits. These ore-element relations derived from a low sample-density survey define priority zones for detailed exploration for significant major massive sulphide deposits.