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Free milling ore evaluation & optimisation

Comprehensive worldwide experience

Most gold projects fall into the free milling category, whereby the ore is milled to liberate the gold prior to leaching and recovery processes. Free milling process work includes the evaluation and optimisation of all relevant process parameters that influence the CAPEX and OPEX for a gold project. ALS Metallurgy, in Perth Western Australia, has conducted thousands of free milling gold projects and no other laboratory group can offer this sort of experience to meet your needs.

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Free milling process testwork services

Overwhelmingly, most gold projects centre around extraction via cyanidation and gold recovery via either carbon in pulp (CIP) or carbon in leach (CIL). The journey of process development usually starts small with a few tests on a blended composite to ascertain general amenability of the ore to these processes. Typically, thereafter, scopes of work expand to much larger programs to encompass wide ranging testing on various ore types and mine domains and leading to comprehensive variability testing once key processing parameters have been established.

After sample preparation, the general order of free milling gold evaluation is as follows:

It doesn’t stop there when your ores are not directly suited to standard processes. This might be due to gold that is finely disseminated in pyrite and requires prior flotation and ultra-fine grinding prior to cyanidation. Ores containing soluble copper can have very high cyanide consumption. Ammoniacal cyanidation can dramatically reduce the overall level of cyanide consumption and we can carry out leach tests to optimise reagent conditions. Ores rich in silver may be better suited to gold recovery from solution via the Merrill-Crowe zinc cementation method. Whatever the requirement, our expertise covers all aspects of processing non-standard ores, from flotation to selective leaching, CIP, elution and fully integrated electrowinning circuits.


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ALS understands that every gold program needs a tailored testing flowsheet specific to the ore.

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Here are some frequently asked questions

Associated testwork services

Related testwork

Gold ores and the associated free milling metallurgical testwork results very often don’t fit into nice categories and packages and will often require other testwork, such as:

Click on the above links or contact us for further information. We can integrate a full program for you if required.