Sediment-hosted Pb-Zn (SH Pb-Zn) deposits can be divided into two sub-types: 'clastic-dominated lead-zinc' (CD Pb-Zn) ores hosted in shale, sandstone, siltstone, mixed clastic or as carbonate replacement within a clastic dominated sedimentary sequence and Mississippi Valley-type (MVT Pb-Zn) ores that occurs in platform carbonate sequences, typically in a passive margin tectonic setting. The emergence of CD and MVT deposits in the rock record between 2.02 Ga, the age of the earliest known deposit of these ores, and 1.85-1.58 Ga, a major period of CD Pb-Zn mineralization in Australia and India, corresponds to a time after the 'Great Oxygenation Event' (GOE) ca 2.4 to 1.8 Ga. Contributing to the blooming of CD deposits at ca 1.85-1.58 Ga was the following: a) enhanced oxidation of sulfides in the Earth's crust that provided sulfate and lead and zinc to the hydrosphere; b) development of major redox and compositional gradients in the oceans; c) first formation of significant sulfate-bearing evaporites; d) formation of red beds and oxidized aquifers: e) evolution of sulfate-reducing bacteria; and f) the formation of large and long-lived basins on stable cratons. A significant limitation imposed on interpreting the secular distribution of the deposits is that presently, there is no way to quantitatively evaluate the removal of deposits from the rock record through tectonic recycling. Considering that most of the sedimentary rock record has been recycled, probably most SH Pb-Zn deposits have also been destroyed by subduction and erosion or modified by metamorphism and tectonism so that they are no longer recognizable. Thus, the uneven secular distribution of SH Pb-Zn deposits reflects the genesis of these deposits, linked to Earth's evolving tectonic and geochemical systems, as well a record severely censored by an unknown amount of recycling of the sedimentary rock record.

An examination of the New Cobar-Chesney-New Occidental area in 1947 concluded that the discordant contact between slaty and sandy beds in the area was a feature of major importance in ore localisation. Accordingly, an investigation was conducted in the vicinity of Cobar to determine whether a relationship existed between discordant contact and ore formation in that area, and to commence a detailed geological map on a regional scale of the Cobar-Nymagee mineral belt. The general geology, character of the discordant contact, stratigraphy, and economic geology of the area are discussed in this report.

The enquiry into this mine resulted from an application by the company for a loan from the Commonwealth to carry out exploration and development. The Tindalls Gold Mine has not been examined by the Bureau and unless this is done no definite statement about the ore possibilities of the property can be made. However, from past reports it seems likely that the deposit has a chance of producing a large tonnage of ore. Under present conditions and with the mining methods now employed, it is extremely doubtful whether ore of this grade could be mined at a profit. The ore reserves, mining, milling, costs, and general financial outlook with respect to the mine are discussed in this report.

Summary report on the ore prospects of some Western Australian gold mines. The report provides details on production, ore deposits, and operations.

The Blue Spec Mine, Nullagine, was visited from 20th to 24th September, 1947. An inspection was made of the mine. No. 3 level (depth 450 feet) was mapped and the antimony-gold occurrences on lease 196, and on the property known as "Blacks", were also briefly inspected. The present position regarding water supply was investigated and recommendations made. The ore reserves, workings, economic considerations, and water supply are discussed in this report.

These notes are supplementary to an earlier report (1948/016), and are designed to elucidate certain points brought up in that report. The issues of grade, workings, development, expenditure, production, and future prospects are generally discussed.

The geology and ore reserves of the dolomite deposit near Wall's Siding are discussed in this report. The report should be read in conjunction with the report on "Limestone and Dolomite Deposits at Cow Flat and Wall's Siding, New South Wales" (Record 1947/090).

This geophysical survey was undertaken as part of a campaign by the N.S.W. Mines Department and the Commonwealth Bureau of Mineral Resources to explore the ore possibilities of the Cobar Mining Field. Tests, made in January 1947, on specimens of ore from the operating mines showed that some of the ore from the New Cobar and Chesney Mines exhibited appreciable magnetisation due to its pyrrhotite and possibly magnetite content. The survey was commenced in March, 1947 using the magnetic method only as a first method of attack. Watts Vertical Force Variometers Nos. 15887 and 16128 were used, the field work being carried out by the writers. The geology of the area, object of the survey, results, and recommendations for future drilling are discussed in this report. Two accompanying plans are included.

The present report gives an overview of the general geology and ore geology of the Blue Spec Mine. The main orebodies are described in some detail. General estimates of reserves and recommendations for future geological work are noted.

The operational history, orebody, workings, grade, tonnage, and financial considerations relating to the Chesney mine are discussed in this report. Two geological plans are included.