Reef exploration in the East Sengkang Basin,Sulawesi, Indonesia

Reconnaissance seismic shot in 1971/72 showed a number of well defined seismic anomalies within the East Sengkang Basin which were interpreted as buried reefs. Subsequent fieldwork revealed that Upper Miocene reefs outcropped along the southern margin of the basin. A drilling programme in 1975 and 1976 proved the presence of shallow, gas-bearing, Upper Miocene reefs in the northern part of the basin. Seismic acquisition and drilling during 1981 confirmed the economic significance of these discoveries, with four separate accumulations containing about 750 × 10⁹ cubic feet of dry gas in place at an average depth of 700 m. Kampung Baru is the largest field and contains over half the total, both reservoir quality and gas deliverability are excellent. Deposition in the East Sengkang Basin probably started during the Early Miocene. A sequence of Lower Miocene mudstones and limestones unconformably overlies acoustic basement which consists of Eocene volcanics. During the tectonically active Middle Miocene, deposition was interrupted by two periods of deformation and erosion. Carbonate deposition became established in the Late Miocene with widespread development of platform limestones throughout the East Sengkang Basin. Thick pinnacle reef complexes developed in the areas where reef growth could keep pace with the relative rise in sea level. Most reef growth ceased at the end of the Miocene and subsequent renewed clastic sedimentation covered the irregular limestone surface. Late Pliocene regression culminated in the Holocene with erosion. The Walanae fault zone, part of a major regional sinistral strike-slip system, separates the East and West Sengkang Basins. Both normal and reverse faulting are inferred from seismic data and post Late Pliocene reverse faulting is seen in outcrop.     

Optimization of grid-drilling using computer simulation

A computer simulation method has been developed to find efficient drilling grids for mineral deposits. A well-known ore deposit is used as a model to develop an efficient pattern for undiscovered ore bodies in the same area or in other prospects where similar geometry is suspected. The model for this study is the Austinville, Virginia deposit, a Mississippi Valley-type deposit composed of 17 ore bodies totaling 34 million short tons (30 million metric tons). The method employs a computer program that simulates drilling the model deposit with different patterns, including various levels of follow-up drilling. Follow-up holes are drilled in fences at one half the original spacing around holes in the grid that show ore-grade mineralization. Each pattern is drilled 100 times from random starting locations to provide a range of outcomes of drilling, including the best, worst, and most likely. For this study, patterns of 100 drill holes were composed of 10 fences spaced 1000–5000 feet (305–1524 m) apart, each with 10 holes spaced 200–1000 feet (61–305 m) apart. In all, 25 grids were used with zero to three levels of follow-up drilling. The 600/2000 grid, with drill holes spaced 600 feet (183 m) apart in fences spaced 2000 feet (610 m) apart, was compared with the 200/5000 grid because they represented contrasting outcomes. The 600/2000 grid penetrated many ore bodies consistently but with few multiple hits to individual ore bodies; whereas the 200/5000 grid inconsistently penetrated few ore bodies with many multiple hits. The 600/2000 grid was more efficient than the 200/5000 grid at hitting large ore bodies of 1,000,000 short tons or greater (900,000 metric tons or greater) and was made more effective by adding one cycle of follow-up drilling. The 600/2000 grid had a 97% chance of hitting one or more large ore bodies with at least one drill hole per ore body, and the 200/5000 grid had a 64% chance. Once hit, there was an 82% chance that the largest ore body would be penetrated by three or more holes when using the 600/2000 grid and an 88% chance using the 200/5000 grid.     

WEKU – a GIS-Supported stochastic model of groundwater residence times in upper aquifers for the supraregional groundwater management

 The supraregional GIS-supported stochastical model, WEKU, for the determination of groundwater residence times in the upper aquifers of large groundwater provinces is presented. Using a two-dimensional analytical model of groundwater flow, groundwater residence times are determined within two extreme cases. In the first case, maximal groundwater residence times are calculated, representing the part of groundwater, that is drained by the main surface water of a groundwater catchment area. In the second case, minimal groundwater residence times for drainage into the nearest surface water are determined. Using explicit distribution functions of the input parameters, mean values as well as potential ranges of variations of the groundwater residence times are derived. The WEKU model has been used for the determination of groundwater residence times throughout Germany. The model results – mean values and deviations of the groundwater velocity and the maximal and minimal groundwater residence times in the upper aquifers – are presented by general maps and discussed in detail. It is shown that the groundwater residence times in the upper aquifer vary regionally, differentiated between less than 1 year and more than 2000 years. Using this information, the time scales can be specified, until measures to remediate polluted groundwater resources may lead to a substantial groundwater quality improvement in the different groundwater provinces of Germany. With respect to its supraregional scale of application, the WEKU model may serve as a useful tool for the supraregional groundwater management on a state, federal or international level. Received: 15 August 1995 · Accepted: 15 October 1995     

Are South China granites special in forming ion-adsorption REE deposits?

Ion-adsorption REE deposits associated with clay minerals are the main global HREE producer. The majority of these deposits are formed by the weathering of granites in South China, but whether there is any fundamental difference between the granites in and outside South China is still unclear. Besides, an effective evaluation system of granite mineralization potential is urgently needed for HREE exploration.To answer this question, we compiled a global granite geochemical dataset from within (n = 1932) and outside (n = 6109) South China, together with a dataset of representative REE deposits in South China (n = 128). The geochemical comparation shows that the South China granites share similar REE contents with those of many granites from places outside South China. Such similarity has also been found between REE ore-related and ore-barren granites in South China. This shows that granites from outside South China could also have ore-forming potential. Warm humid climate and quasi-equalized crustal state promote chemical weathering to continuously leach REEs and store them in the weathering crust. The enrichment ratio (Rx) can be used to quantify the climatic effect between orebodies and parent rocks. The calculated average Enrichment Ratios (Rx) of LREE- and HREE-rich deposits are 2.41 and 2.68, respectively. Sufficient REE content in granite is the prerequisite for mineralization, and we propose that the combination of the minimum REE + Y (172 and 108 ppm in LREE- and HREE-rich parent rocks, respectively) and REE oxide ratio (1.32) can reveal the granite metallogenic potential. Together with the suitable tropical and temperate climate area with ion-adsorption REE deposits, we further identified certain regions with high REE mineralization potential outside South China to assist future exploration.     

2006年新疆地质矿产勘查进展及2007年工作要点

2006年是新疆地质矿产勘查“十一五”规划实施的第一年,地质勘查投入进一步加大,钠硝石找矿取得了重大突破,铁、铅锌、铜镍及煤的找矿也取得了重要进展,基础地质工作程度进一步提高,高新技术方法的应用得到加强,“环准噶尔”和“环塔里木”控制铜、铜镍、铅锌、铁等矿床重要成矿类型的规律逐渐显现.2007年将突出“环准噶尔”和“环塔里木”两个新领域的找矿工作,加快构建基础科研、高新技术应用研究、矿产勘查等相配套的科学的地质勘查体系.