MINERAL EXPLORATION — CASE STUDIES — Winspear adopts systematic approach

Winspear Resources (WSP-V) is showing no signs of letting up on its year-round schedule of diamond exploration in the Northwest Territories.

Since 1992, the Vancouver-based junior and its partners have spent more than $20 million on exploration. Their efforts led to the discovery of two diamondiferous kimberlite pipes and a complex kimberlite dyke and breccia system at the Camsell Lake property, plus the diamond-bearing Nicholas Bay kimberlite pipe on the Aylmer Lake West property.

In the process, the company has collected and processed more than 5,600 till samples, flown over 60,000 line km of airborne geophysics and 1,500 line km of ground geophysics, and completed in excess of 25,000 metres of diamond drilling. The Arctic climate makes is necessary to divide the work into two main seasons. Summer programs typically centre on till or soil sampling, whereas the bulk of the drilling is carried out during the winter, when lakes, which often coincide with potential kimberlite targets, are covered by up to 5 ft. of ice, allowing drill access.

Basal till sampling of glacial debris enables operators to locate source areas for kimberlites. Till or soil samples, weighing about 25 kg, are collected along traverses perpendicular to the known glacial ice dispersion.

The samples are processed and studied for the presence of kimberlite indicator minerals, a specific suite of minerals that form at depths coinciding to diamonds, but at much greater concentrations. These kimberlitic indicator minerals include pyrope garnets, picroilmenites, chrome diopsides, chromites and olivine.

If positive results are obtained, additional till samples are collected “up-ice” until a likely source area is isolated.

In the field, Winspear uses a unique method of panning till samples for kimberlite indicator minerals. The method was introduced to the company by Nickolai Pokhilenko, who is the chief research geologist for the Russian diamond company Almazy Rossii Sakha and also head of the Laboratory for Diamond Deposits, Institute of the Russian Academy of Sciences, in Novosibirsk.

Pokhilenko helped Winspear locate the CL-25 kimberlite pipe on only his second day at Camsell Lake, back in 1994.

The panning technique involves initially using lake water to wash and sieve the 25-kg till sample through a 2-mm screen. The plus-2-mm material is discarded and, using a wooden pan, the minus-2-mm material is panned to remove the lighter fraction. The sample is then dried and further sieved to remove both fine and coarse material. The sieved material is then shipped for treatment by heavy liquid processing to produce a concentrate of heavy minerals. This can be done in a 7-to-10-day turnaround.

If a quick turnaround time is not required, Winspear will ship the till samples directly to an outside mineral processing laboratory, without panning the samples first.

During the processing of the till sample, the initial 25-kg is reduced to a 1-to-30-gram sample of discrete mineral grains, which is then “hand-picked” in the field by an in-house team of experienced mineralogists.

Picking is a time-consuming and tedious task that involves the use of a binocular microscope to examine all the grains in the sample and identify all kimberlite indicator minerals. Winspear’s mineralogists can pick through approximately five small samples per day.

Geophysical surveys are carried out in an effort to detect kimberlite bodies whose physical, electrical and magnetic properties may differ from the surrounding country rock. Airborne surveys are first flow over large areas on a pre-established grid. Electromagnetic-magnetic (EM-mag) and mini-mag surveys are normally flown. Follow-up ground horizontal loop electromagnetic (HLEM) and magnetic surveys are done to provide greater detail and a finer resolution.

The kimberlite pipes found in the Northwest Territories have demonstrated a wide range of geophysical responses, from none to bold and distinct.

Bathymetric surveys are conducted to measure the depth of the lake bottoms.

This process provides a view of possible erosional features.

Drilling is the final and most costly component in kimberlite evaluation.

Many potential targets lie beneath lakes and, subsequently, most drill programs occur from February to May, when the lakes are frozen. The drill is used to test a wide range of indicator mineral and geophysical anomalies.