Arsenic-rich Zones in Nickel Sulphide Mineralisation

June 2nd, 2016

Introduction

Rönnbäcken nickel project is located in northern Sweden, and was until recently explored by Nickel Mountain Group AB. Drill cores from Rönnbäcken were analysed with Minalyzer CS.

“Minalyze’s technology represents a significant advance in quick geochemistry to support the exploration geologist in her or his endeavours to find deposits viable for mining,” says Johan Sjöberg, Chief Geologist at Nickel Mountain Group AB. “The technology enables you to effortlessly have geochemical data at your fingertips when logging drill core, without the hassle of re-logging the core after sampling and assay at a conventional lab.”

Case study: Arsenic-rich zones in nickel sulphide mineralisation

Rönnbäcken project is an ophiolite-hosted metamorphogenic nickel sulphide deposit, which consists of serpentinised ultramafic lenses that host a measured and indicated resource of 668.3 Mt with an average grade of 0.176 % nickel, of which 0.099 % is nickel sulphide. Nickel sulphide minerals include pentlandite ([Fe,Ni]9S8), heazlewoodite (Ni3S2), and millerite (NiS).

The contact zones of the deposit are commonly enriched in arsenic, hosting minerals such as gersdorffite (NiAsS), orcelite (Ni5As2), and nickeline (NiAs). Arsenic is a troublesome element that is commonly found alongside commodities such as copper, cobalt, nickel, and gold. Due to environmental restrictions, smelters give penalties for ore concentrates that contain significant amounts of arsenic, and reject concentrates with more than 0.5 % arsenic. Arsenic minerals can induce crippling penalties at the smelter, if they are not well characterised and kept out of the nickel sulphide concentrate.

To illustrate the accuracy of the scanning results, they are compared to conventional laboratory assays in Figure 1. The lower contact of the nickel mineralisation is enriched in arsenic.

arsenic

Figure 1 – Comparison of Minalyzer CS analysis results with conventional laboratory assays, illustrating the good accuracy of the scanning results. Arsenic-rich ore can be identified from scanning results.

The scanning results were reported on a higher resolution that the conventional assay intervals.

“Another great advantage is the improved resolution. At Rönnbäcken we typically assayed in two-metre intervals: with Minalyze we can get a resolution that is less than a hundredth of that,” says Johan Sjöberg. “We can actually look at the composition of a vein or alteration band right off the bat.”

The results from drill core scanning with Minalyzer CS not only provide an accurate estimation of the total nickel content, but can also indicate arsenic-rich zones in the mineralisation. Awareness of penalty elements at an early stage allows the geologists to take them into consideration during the whole process of resource characterisation.