Carbonate Hosted Lead Zinc Ore Deposits - Exploration

Exploration

Exploration for MVT deposits is relatively complex in theory and straightforward in practise. During the area selection phase, attention must be paid to the nature of the carbonate sequences, especially if there is a 'dolomite front' alteration identified within oil exploration wells, which is commonly associated with lead-zinc mineralisation.

Thereafter, attention must be paid to picking floral facies of any reef carbonates formed from coral reef accumulations. The facies of the carbonate sequence is critical, as this is controlled mostly by faults which are the ultimate target of exploration. A fore-reef/back-reef transition is the 'sweet spot', and thus depending on the age of the carbonate sequence, familiarity with coral palaeontology is considered essential.

Finally, once a basin model of the carbonate sequence is formulated, and the primary basin-margin faults are roughly identified, a gravity survey is often carried out, which is the only geophysical technique which can directly detect MVT deposits. Gravity surveys aim to detect significant accumulations of lead and zinc due to their greater density relative to their surrounding host rocks.

Finally, the 'pointy end' of an exploration programme is to drill each and every one of the gravity targets in sequence, with no favour or prejudice given to the strength or amplitude of any anomaly. It is well known that unsubtle and unsophisticated methods of pattern drilling have found MVT deposits missed by more selective explorers, for instance the Lennard Shelf Deposits in Western Australia were found on the second last hole of an extensive drilling programme.