A diverse range of mineralisation, including porphyry and epithermal deposits, intrusion-related gold and other metal deposits, iron oxide-copper-gold (IOCG) deposits and orogenic gold deposits all have linkages to crustal growth and magmatic arcs. Furthermore, all of these deposit types are associated with fluids containing H2O, CO2 and NaCl in varying and differing proportions. In all cases, it can be argued that magmas are a key source of hydrothermal fluids for these types of mineral system, and that subduction processes are critical to controlling fluid chemistries, the metal-bearing capabilities of the fluids and depositional processes. The differences on typical/bulk fluid chemistries between deposit types can be explained in part by differences in the P-T conditions of fluid segregation from its magmatic source. The most significant control here is the pressure at which fluid forms from the magma as this has a strong effect on fluid CO2/H2O values. This is clearly exemplified by the rare occurrence of readily detectable CO2 in deep porphyry systems (Rusk et al., 2004). On the other hand, fluid Cl contents (which strongly influence its base metal carrying capacity) are very sensitive to the magma's bulk composition. However, only some subduction-related magmas are fertile, and the differences do not seem to be due solely to variations in effectiveness of depositional processes. So what controls the volatile content of the magmas? Isotopic and other evidence, in particular for S and Cl, shows (unsurprisingly) that the greater contents of these elements in arc magmas compared to other melts is due to contributions from subducted materials, although there may be additional, lower crustal sources of Cl. Variations in the budget of volatiles subducted may thus play a role in controlling the chemistry of magmas and associated hydrothermal fluids, but variations within individual arcs suggests that again this is not the entire story.

Mapping carried out at Kuridala by C.J. Sullivan and R.S. Matheson during the period June 17th-27th has shown that the ore deposits occur in a major fault (and associated lesser shears). The existence of the fault system is considered to have been proved, and it has been traced, with some interruptions over a distance of three miles. It may extend for many miles beyond the present limits of mapping. The geological information given appears to rule out a number of chances of occurrence at shallow depth, formerly considered likely, and thus is somewhat discouraging. However, the work does indicate that repetition deposits are likely to be present and opens up intriguing possibilities.

This report comprises notes on the geology, ores reserves, and exploration of the Maude and Yellow Girl Gold Mining Company.

The Mosquito Creek Wolfram Field was visited on 6th and 7th October, 1951. This report gives a brief account of the inspection. The general geology of the area, the ore-bearing reefs, and the mining leases inspected, are described.

A geological survey of the Peko Gold Mine was conducted as part of the field activities of the Bureau of Mineral Resources in 1950. The objects of the survey were to study the factors localizing the ore, to suggest possibilities for the discovery of new oreshoots, and to plan a diamond drilling campaign to test these possibilities. J.F. Ivanac and B.P. Walpole mapped the geology of the mine. The plane table survey of the surface outcrops was carried out by E.M. Bennet. The results of the survey are presented in this report. History and production, general geology, economic geology, and the prospects of further discovery are discussed.

A geological investigation of the Maranboy Tin Field was commenced by officers of the Bureau of Mineral Resources in May, 1951. The object of the survey is, primarily, to obtain a detailed preliminary assessment of the potential ore reserves of the field. Geological mapping and sampling of the major lode lines has been carried out in an attempt to determine the features which control ore deposition and to enable estimates to be prepared of the grade and tonnage of ore per vertical foot, which may be expected from these lode lines. The main emphasis of this work during the 1951 field season was on the major producing lines in what has been called the Southern Field, the Main Lode and part of the Stannum King lode. In addition to this programme, an area of approximately nine square miles was mapped in detail using aerial photographs. Approximately 1,000 square miles of the area surrounding Maranboy was mapped on a regional basis. The history of the field, general geology, and the geology of the individual lodes are discussed in this report. The accompanying maps are enclosed.

Metallogenic, geologic and isotopic data indicate secular changes in the character of VHMS deposits relate to changes in tectonic processes, tectonic cycles, and changes in the hydrosphere and atmosphere. The distribution of these deposits is episodic, with peaks at 2740-2680 Ma, 1910-1840 Ma, 510-460 Ma and 370-355 Ma that correspond to the assembly of Kenorland, Nuna, Gondwana and Pangea. Quiescent periods of VHMS formation correspond to periods of supercontinent stability. Large ranges in source 238U/204Pb that characterize VHMS deposits in the Archean and Proterozoic indicate early (Hadean to Paleoarchean) differentiation. A progressive decrease in - variability suggests homogenisation with time of these differentiated sources. Secular increases in the amount of lead and decreases in 100Zn/(Zn+Pb) relate to an increase in felsic-dominated sequences as hosts to deposits and an absolute increase in the abundance of lead in the crust with time. The increase in sulfate minerals in VHMS deposits from virtually absent in the Meso- to Neoarchean to relatively common in the Phanerozoic relates to oxidation of the hydrosphere. Total sulfur in the oceans increased, resulting in an increasingly important contribution of seawater sulfur to VHMS ore fluids with time. Most sulfur in Archean to Paleoproterozoic deposits was derived by leaching rocks below deposits, with little contribution from seawater, resulting in uniform, near-zero-permil values of 34Ssulfide. In contrast the more variable values of younger deposits reflect the increasing importance of seawater sulfur. Unlike Meso- to Neoarchean deposits, Paleoarchean deposits contain abundant barite, which is inferred to have been derived from photolytic decomposition of atmospheric SO2 and does not reflect overall oxidised oceans. Archean and Proterozoic seawater was more salty than Phanerozoic, particularly upper Phanerozoic, seawater. VHMS fluids ore fluids reflect this, also being saltier in Precambrian deposits.

This report describes a geophysical survey made in May 1952 and August 1953 at the Silver Valley mine workings, near Inverell, N.S.W. From the workings there is evidence of mineralisation along a well-defined fissure and one ore shoot has already been partly developed. The survey was made in an attempt to locate other ore shoots of sufficient size to warrant mining operations. Self-potential, magnetic and electromagnetic methods were used in the survey. The self-potential method showed a well-defined anomaly on the eastern extension of the fissure, indicating that a small body of sulphides may exist there with its centre about 300 feet east of the known ore shoot. The magnetic and electromagnetic results showed no pronounced anomalies which could be correlated with any defined ore shoot. Recommendations are made as to how the self-potential anomaly could best be tested. These comprise sinking a shaft at the centre of the anomaly, extending an existing adit, or driving a new adit from a point nearer the anomaly.

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.