AUL (ASX) Ann: Drilling Update at Morning Star Gold Mine

Originally posted by Krum: ↑

Sampling and analysis is a scientific area especially for mining and mineral processing. It’s statistical. The bigger the average particle size the bigger the sample required to be representative. Likewise there is a scientific process to crush and sub sample a few times down to a few grams that is bathed in acid to digest the metals for final analysis.

Generally the run of mine ROM product (cannot use the word “ore” without a JORC based economic study under VALMIN code) is sampled at a point in the primary crushing circuit (head grade) and then all product streams (concentrate and tails) are ampled and analysed.

A production mass balance is then calculated where the sum of the products equals the sum of the feed:

(head tonnes x head grade) = (Con tonnes x Con grade) + (Tail tonnes x tail grade)

Obviously the sum should be close to equal (a mass balance close). Also the head grade and tonnes can be back calculated from the sum of Con plus tail.

In a fully transparent report, especially for trial mining, especially for nuggetty material, full correlations from Con and tail grades back to block models from drill results should be made and reported.

For example the average from 3 drill holes might be a minable block of x tonnes at y grade. When mined the ROM is a tonnes of b grade (fed to process plant) from which c tonnes at d grade of Con and e tonnes at f grade tails is produced and it all should back calculate in the mass balance.

So they should have all the data. Why selective pieces of the overall mass balance are available is up to them.

The comparison of the averaged grades from drill holes is the “magic multiplier” used in the old JORC and is important for confidence in mining or not decisions and also important to optimise (reduce) the amount of $ spent on infill drilling before confident mining.

All the VIC nuggetty mines I know of have their economic basis tied to optimising the cost of drilling vs mining. Many mines die due to too much money spent drilling.

AUL may have decided to just sample and analyse Con and tail and back calculate head to compare to modelled average drill grade.
But I reckon they would have sampled head grade and also back calculated it so why not release the full mass balance?

Also the splits between coarse free gold and sulphides or arsenopyritic gold should be known (80/20?) noting the coarse free gold goes to their own gold room and the sulphides can be treated or sold by refiners.
KRUM

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I'm thinking they won't release the RoD head grade as the recoveries are pretty poor, this line in the quarterly confirms that imo.

"During the quarter, various process improvements have been tested at a bench test level to identify ways to lift recoveries. As a result additional equipment is being hired to assess improved recovery opportunities in a full plant trial. "

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