2017 gold deposits boasting the highest grade drill intersects

By analyst

By Vladimir Basov

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Drill results are important indicators not only for mining and exploration companies, but nearly all stakeholders involved, including existing shareholders and potential investors.

While high-grade drill intersects are generally exciting and promising news, a conservative and very rigorous approach is recommended when a non-technical person is trying to understand the results of a drilling campaign.

It is not uncommon to see a press release where a company proudly claims that a “significant” interval has been recently intersected and that contains, for example, a 5,000 g/t gold grade. Such news can rapidly increase a company’s stock price, but is grade alone the crucial factor in a drill results’ interpretation?

Actually, these super-high anomalous grades are often associated with very narrow drill intervals, which may be caused by a nugget effect. These high grades may not adequately represent the composition of the ore body (if any), and cannot necessarily be considered as reliable precursors of a high-grade ore body or a deposit as a whole (Note: caution should be taken when the first drill results are reported from a greenfield project, especially when the type of mineralization and ore continuity/morphology are still unknown).

As such, when considered alone, high-grade drill intersections sometimes fuel speculation which may not show the real representative picture of the deposit. They should be considered mainly as a teaser that spurs further in-depth research and technical reports.

Other factors must be taken into consideration while interpreting drill results. The most important of them is the width of ore interval(s) intersected by the drill hole.

Indeed, a drill hole with a wide interval of mineralized material at a lower grade can be very beneficial to the company and often far more valuable than a high-grade drill hole intersection but with narrow width.

Moreover, narrow high-grade intersects may not be representative of the extent and continuity of the whole ore body, and may not be even part of a bigger ore body because of the “outlier” samples effect. At the same time, wide intervals of lower ore grade can be precursors of a massive deposit.

Narrow ore bodies are usually mined by expensive, selective mining methods, while massive wide ore bodies can be exploited using effective, lower-cost and highly productive bulk mining methods.

When combined with grade, the width of a drill intersect is a powerful tool that can be used to compare drill results released by different companies. When applying a gram-metre technique (grams per tonne of drill intersection at 1m intervals multiplied by the length of drill hole above the cut-off grade), the following concepts should also be used:

True width

Exploration drill holes are not always vertical and can, in fact, be drilled at any angle. Deposits can be of any imaginable shape and orientation, too. Consider a worst-case scenario, where a nearly vertical drill hole intersects a nearly vertical ore body or a nearly horizontal hole intersects a nearly horizontal ore body (usually when exploration holes drilled from underground workings). In this case, if a …read more

Source:: Infomine

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