Improving lithological discrimination in exploration drill-cores using portable X-ray fluorescence measurements: (2) applications to the Zn-Cu Matagami mining camp, Canada

Abstract

A new geoscientific application of portable XRF (pXRF) analysers is the acquisition of high-spatial resolution down-hole geochemical profiles obtained in-situ on exploration drill-cores. One advantage of such profiles over traditional laboratory geochemistry, apart from the non-destructive aspect of pXRF, is that they are obtained quickly, in the field. So they can help exploration companies take important decisions such as “has a target stratigraphic horizon been reached, or should we drill deeper?” For example, in the Matagami mining camp, pXRF data permits the rapid distinction of two visually similar and variably altered rhyolites in the Persévérance area, based on a plot of Ti/Zr vs Al/Zr. The corrected pXRF data plot within the same fields as the traditional geochemical analyses for these rhyolites. Another advantage of pXRF profiles for exploration companies, geological surveys or academic researchers is the ability to locate lithological contacts better, and in general improve down-hole lithological discrimination, especially for fine-grained and/or hydrothermally altered lithologies. For example, in the Caber volcanogenic massive sulphide deposit area, there are abundant intrusions which makes it difficult to follow the volcanic stratigraphy between drill-holes and sections. In the drill-hole studied, the pXRF data, plotted as down-hole profiles of elements/oxides and ratios, allow several previously unidentified altered dykes to be distinguished from altered rhyolites.

Portable X-ray fluorescence measurements on exploration drill-cores: comparing performance on unprepared cores and powders for ‘whole-rock’ analysis

“…For example, if the goal is to obtain highspatial resolution downhole geochemical profiles on entire drill holes, then in situ measurements with smoothing (e.g. three to five point moving averages) provide fit-for-purpose data (Ross et al 2013(Ross et al , 2014b.…”

“…Such strategies can become time consuming and Fischer et al (2014) and Simandl et al (2014) noticed negligible drift, leading to doubts about the necessity of investing substantial time on measuring CRMs every hour or every 20 samples. This paper, building on the work of Ross et al (2014aRoss et al ( , 2014b, continues the performance study of two pXRF analyzers used on non-mineralized to weakly mineralized rock core samples. The main focus here is on comparing the performance of the devices on a series of rock core samples, both in situ and in powdered form.…”

“…In the latter field, the focus so far has been on analysing pulverized rock samples or performing the equivalent of assays on drill-cores (Glanzman & Closs 2007;Peter et al 2009;Fajber & Simandl 2011;Marsala et al 2011). Ross et al (2014aRoss et al ( , 2014b have also looked at performing, in situ, the equivalent of whole-rock analyses on drillcores to produce high spatial-resolution elemental profiles.…”

“…Instead of taking measurements close together on a core sample and average them, it is possible to take measurements at regular intervals along the core and smooth the data with a 3-point or 5-point moving average (Ross et al, 2013(Ross et al, , 2014b. This assumes that geological units are much thicker than the measurement interval, which would typically be the case for lava flows or thick sills for example.…”

High-Resolution Physical Properties, Geochemistry, and Alteration Mineralogy for the Host Rocks of the Archean Lemoine Auriferous Volcanogenic Massive Sulfide Deposit, Canada

“…The logger also acquires a continuous image of the core using a line-scan camera. Our methods have been described in detail by Ross et al (2013Ross et al ( , 2014bRoss et al ( , 2014c and references therein, with recent improvements for geochemistry presented by Bourke and Ross (2015). LEM-37 is a 894.2 m-long BQ (3.7 cm diameter core) drill hole; the cored portion starts at 5.5 m, for a total core length of 888.7 m. We have obtained a total of 3486 measurements of density, magnetic susceptibility, and infrared spectrometry in this hole, for a downhole resolution (average measurement spacing) of 25.5 cm.…”