22-1/H55-9/12 Vertical scale: 5

No abstract available

10% coverage sth west 22/E55/36 Vertical scale: 1000

22-1/H54-7/13 Vertical scale: 100

The format of most existing metallogenic maps is not adequate for scales of 1:500 000 or less. The major problem is the colourful out-of-scale locality symbols, which mask the map detail in the most important areas, the immediate vicinity of the ore occurrences. The design of the symbols is also a problem, most being influenced considerably by genetic interpretations that are subjective and change with time; they are incapable of expressing transitionality, correlation of metallogenetic and lithogenetic events, and they cannot accommodate incomplete information. A substantially different philosophy of metallogenic mapping has been tested using the Pine Creek Geosyncline as an example. Ideally, the product would be a set of three matching maps. Map 1 would be a base map, a modified geological map that consistently shows the age of units by colour and the lithology of units by pattern, regardless of genesis and the level of emplacement. Mineralised occurrences would be identified in the simplest way possible, so as not to obscure the background information. Map 2 would be a gitological map, or map of mineral deposits, providing information on the geological properties of occurrences. The symbols suggested are based on simplified geological cross-sections, and are colour and pattern coordinated with the base map, to give the reader an immediate impression about the contemporaneity of rock-and ore-forming events and of the hosts to the ore. Within the symbol framework for a given mineralisation style, a wide range of properties of individual occurrences can be shown, and unknown information can be truthfully expressed as a blank component of the symbol. Map 3 would be a commodity map, showing the ore metals, their individual and total accumulations, and the concentration of the major metal.

Entropy-ratio maps enable mapping of surficial facies of coral reefs at any chosen resolution. A ternary classification uses detritus, framework encrustation, and pavement as end-members, and is subdivided on the degree of mixing of these. The classification is sensitive to all reef environments, particularly to zonation across reef flats. It can also be superimposed on other classifications. An example is given of its use in the Great Barrier Reef.

The results of a gravity and magnetic survey of Niue Island, a raised atoll in the southwest Pacific Ocean, indicate that volcanic rocks underlie the coral limestone capping at a depth of 300-400 m below sea level. A roughly flat-topped, dome-shaped dense volcanic core, is present beneath the southwest of the island. The core has a lateral density contrast of 0.20 t/m3 and a reverse magnetisation of 3.0 A/m, and is believed to be of basaltic composition. An early-middle Miocene age is inferred for the volcanic pedestal. The asymmetric location of the core within the island is thought to be evidence for large-scale landslide activity, particularly on the west and south flanks of the seamount.

A heavy-mineral survey of the Forsayth 1:100 000 Sheet area, north-east Queensland, is described. The suitability of the technique for detecting gold, tin, and probably uranium mineralisation in the region has been established. The heavy-mineral method is also useful in the interpretation of sieved-sample surveys, and can provide valuable input to geological and metamorphic mapping programs.

Geothermal gradients in Australian sedimentary basins have been calculated from data obtained from water bores in the Great Artesian Basin and oil exploration wells. The data are subject to several types of systematic error, but statistical trends have been extracted, using values of thermal conductivity obtained from sediment compaction models. Estimates of heat flow from the Great Artesian Basin are consistent with the configuration of the major aquifer systems. Oil well data confirm the regional trends obtained from previous investigations, but previously recognised anomalies in southeast Australia are no longer evident. Temperatures at a depth of 40 km range from 320°C to 380°C for the Precambrian terrain and from 470°C to 550°C for the Phanerozoic . These results are modified by sediment cover. A 1 km thickness causes additional heating, with temperatures raised by 16-40°C.

The contact between the middle Proterozoic Mitchiebo Volcanics and Top Rocky Rhyolite, in the Carrara Range Region of the Northern Territory, is highly irregular and is interpreted as a disconformity. Sandstones in the Mitchiebo Volcanics were lithified and then eroded into a series of narrow ravines up to 120 m deep. Rhyolitic ignimbrite and lava blanketed and preserved the irregular surface. The preservation of the surface provides us with a rare glimpse of middle Proterozoic landforms.