The Irish occurrence is situated at the south end of the Mitchell Range, approximately 5 kilometres east of Nesbut Peaks and 40 kilometres southeast of Takla Landing. It comprises occurrences X1-X2 as outlined by Whittaker (Fieldwork 1982-1, Table 1) and is the largest of numerous chromite occurrences located in the range (see 093N 033, 34, 36, 37, 38, 39, 40).
The area is underlain by allochthonous serpentinized ultramafics, formerly assigned to the Middle Permian to Late Triassic Trembleur intrusions, and now termed Mississippian to Triassic Oceanic Ultramafites. These rocks host local pre-tectonic orthopyroxenite veins, both pre- and post-tectonic gabbro dikes and "alteration dikes" of albitite-rodingite. The massif is bound by north-northeast and east-trending lineaments and is both surrounded by, and hosts xenoliths of sedimentary rocks assigned to the Carboniferous to Jurassic Cache Creek Complex. Late Triassic-Early Jurassic Topley intrusions have been emplaced into the Cache Creek Complex rocks immediately west and north of the allochthon.
The allochthon comprises widely serpentinized, tectonized harzburgite with minor dunite. The harzburgite is a mottled black-green to black-brown colour on fresh surfaces and is generally intensely foliated. It weathers to a deep brown colour with pale, silvery brown talcose patches. The dunite comprises fine to medium-grained anhedral olivine occurring in contorted, irregularly shaped patches that reflect the internal deformation of the harzburgite. Xenoliths up to one square kilometre in area commonly occur in the southern part of the massif and consist of limestone, dolostone, siltstone with chert laminae and shaly siltstone. Smaller xenoliths occur to the north.
Fine to medium-grained chromite is common as disseminations throughout the ultramafic rocks, varying from trace to two per cent by volume. Harzburgite, however, hosts all but one of the layered and nodular aggregate and massive chromite occurrences in the area, including the Irish (Fieldwork 1982-1, page 237).
Early reports describe mineralization at the Irish occurrence as comprising several irregular lenses of chromite hosted by serpentinized harzburgite distributed over a strike length of 20.7 metres along a line trending 154 degrees. The largest of these lenses was reported to be 9.9 metres long and averages 2.7 metres wide and the total area of exposed chromite was estimated to be approximately 36 square metres (Geological Survey of Canada Memoir 252, page 190). Later work carried out in the area, however, identified only two aggregate (greater than 75 per cent) chromite nodules, the largest of these being 8 by 4 centimetres (Fieldwork 1982-1, Table 1). This nodule reportedly trends 027 degrees.
Average assay values from 17 channel samples reportedly taken from several lenses across an average width of 1.68 metres are: Cr2O3 35.6 per cent, Cr 24.3 per cent, Fe 10.7 per cent (Geological Survey of Canada Memoir 252, page 190).
Work History
Chromite was identified in the area by at least the early 1940s. Little or no other work is reported until at least the 1980s.
In 2004 four two-post claims were staked by Ursula Mowat to cover 4 of 17 previously known chromite showings. Five rock samples were collected from the IR claim which covered the Ireland showing. Results of the sampling (on all claims including OS, PT and PD) were reported to be disappointing in that no chromite was located and the rock samples that were analyzed contained no significant PGE values. Elevated nickel values were encountered in the ultramafics especially on the IR and PD claims. Only the IR claim covered a previously known showing in the area. Samples B158724 through B158729 from the IR claim yielded values from 0.146 to 0.196 per cent nickel and 0.042 to 0.104 per cent chromium (Assessment Report 27857).
In 2009, FPX Nickel Corp. prospected and sampled the area as the Mesa 8-14 claims.
