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Old-time prospector

Old-time prospector Billy Capp from Lightning Ridge, NSW

Mineral exploration for opals is termed prospecting, conducted under an Opal Prospecting Licence or Mineral Claim. Opal Prospecting Licences are granted over much larger areas than those granted under mineral claims but are purely for prospecting and do not authorise mining.

An Opal Prospecting Licence can only be granted over lands defined as an "Opal Prospecting Block" within an area designated under the Mining Act 1992 as an "Opal Prospecting Area". There are several Opal Prospecting Areas in the Lightning Ridge and White Cliffs Mineral Claims Districts.

A dramatic increase in the level of prospecting around Lightning Ridge occurred in the late 1980s with the introduction of the nine-inch auger drill which provided means of drilling a large number of holes relatively cheaply and quickly.

Opal Prospecting Licences are handled by the department's Lightning Ridge Office.

Opal Prospecting Areas (OPAs)

Opal mining at Lightning Ridge takes place within Opal Prospecting Areas (OPAs) which are within the Narran–Warrambool reserve. There are currently four opal prospecting area (OPAs 1–4) designated within the Narran–Warrambool Reserve. Download a Map of Lightning Ridge OPAs (7.8 MB PDF)

The Narran–Warrambool Reserve was established over the Lightning Ridge Mineral Claims District in 1993, covering approximately 5000 square kilometres of land surrounding the Lightning Ridge opal fields. The reserve was designed to protect the heritage of the small miner by preventing the granting of large exploration licences and mining leases, effectively limiting operations to small scale mining. Only mineral claims, Opal Prospecting Licences and mining leases for mining purposes are allowed to be granted.

  • Land may not be constituted as an opal prospecting area or added to an existing opal prospecting area:
  • if an application for an authority is pending in respect of the land, or
    • if an authority is in force in respect of the land, or
    • if the land forms part of a reserve, an exempted area, a mineral allocation area for opal or a colliery holding, or
    • if it has been determined in accordance with Schedule 2 that the land is agricultural land.
  • Land that is within a national park, state conservation area, regional park, historic site, nature reserve, state game reserve, Aboriginal area, protected archaeological area, wildlife district, wildlife refuge, wildlife assessment area or Aboriginal place within the meaning of the National Parks and Wildlife Act 1974 may not be constituted as an opal prospecting area, or added to an existing opal prospecting area, except with the consent of the Minister administering that Act.

Opal prospecting methods

Opal is found by working underground from shafts, by auger/percussion drilling, by geophysical method, or by treating old dumps that surround shafts. Prospecting methods used are extremely variable.

Shaft sinking

Until about 1987, most of the prospecting on the opal fields was carried out by sinking a shaft to intersect the claystone, then developing drives horizontally to test the value of the opal dirt. The shafts were traditionally sunk by hand or by Caldwell drill. The process is relatively slow and costly.

Auger drilling

The end of the 1980s saw the rapid introduction of the 230 mm (9") diameter auger drill. This technology redirected the emphasis in prospecting away from shaft-sinking to gain access to the opal clays, toward testing for the existence of the necessary overlying sandstone, and looking for colour in the small sample of clays that the auger drill produced.

In most cases, the use of auger drills to assess the opal-bearing potential of an area is quicker and more cost-effective than shaft-sinking. Layers of silcrete up to a few metres thick, which are common on plateau areas, slow the rate of drilling considerably. Silcrete may occur as large slabs that are more or less continuous, or as scattered boulders through the soil profile.

In 2002, the department recorded an average of 28 holes drilled per Opal Prospecting Licence. The number of holes drilled is only restricted by the miner's budget with prospectors generally drilling between 10 and 100 holes on a given licence. Prospectors are required to backfill test holes in accordance with department's standards.

Percussion drilling

Smaller-diameter (>120 mm) percussion drilling rigs have also been used in recent years with some success. Although they create a smaller hole, with smaller samples than auger drills, they are quicker and readily penetrate silcrete.

Prospectors are required to backfill percussion drilling holes in accordance with department's standards

SIROTEM — a geophysical method

In 1986, the Geological Survey of New South Wales trialed the geophysical method, SIROTEM, on the opal fields. This technique uses electrical current to measure the varying resistance of the underlying rocks, and in doing so, provides information that can be readily interpreted to indicate where sandstone, claystone and faults are likely to exist. The benefits of this method are that large areas of ground can be tested quickly to provide a comparative assessment of the areas before drilling.

In more recent times, ground radar has been trialled as a means of identifying areas with potential for opal-bearing clays.

These geophysical techniques remain in their infancy as far as the opal fields are concerned, but have the potential to become an important tool for the opal prospector.

Opal prospecting licences

Opal prospecting licences are granted for the purpose of exploring for opal over opal prospecting blocks (OPBs) which divide the OPAs 1, 2, 3 and 4.

Area

Applications must be in respect of designated opal prospecting blocks within an Opal Prospecting Area. The size of blocks vary but do not exceed 500 hectares.

Duration

Opal prospecting licences are granted for a period of either 28 days or 3 months over designated opal prospecting blocks at Lightning Ridge and White Cliffs.

Conditions

There are conditions for opal prospecting licences in the individual opal prospecting areas:

Fees

In accordance with Schedule 8 of the Mining Regulation 2016, lodgement fees are payable in addition to an administrative levy. Visit the Lightning Ridge fees and charges web page.

Opal prospecting reporting

At the end of the term of an opal prospecting licence, a report covering all prospecting done must be submitted.

A template has been prepared to aid in the preparation of these reports. One side of the form consists of blank columns for graphic logs of the results of all drilling or shaft sinking. The logs should show the depth to, and thickness of, each different rock type. Download the Opal prospecting reporting - drillhole logging template (58 KB PDF).

All intersections of opal, whether precious or potch, should be noted on the logs. The reverse side of the form has instructions on the preparation of a location map to be provided with the logs.

It is recommended to submit the opal prospecting licence reports in digital format although it is not a requirement specified in the Mineral Exploration Reporting Guide.

Scanned copies of opal reports can be retrieved from DIGS®

For further information
Lightning Ridge Office
Phone:
+61 (0)2 6829 9200
Fax:
+61 (0)2 6829 0825
LightningRidge.Office@industry.nsw.gov.au
Postal:
NSW Department of Planning and Environment, Division of Resources and Mining, PO Box 314 Lightning Ridge NSW 2834
Office:
60 Morilla Street Lightning Ridge NSW 2834 Map