Evidential belief functions for data-driven geologically constrained mapping of gold potential,Baguio district,Philippines

A data-driven application of the theory of evidential belief to map mineral potential is demonstrated with a redefinition of procedures to estimate evidential belief functions. The redefined estimates of evidential belief functions take into account not only the spatial relationship of an evidence with the target mineral deposit but also consider the relationships among the subsets of spatial evidences within a set of evidential data layer. Proximity of geological features to mineral deposits is translated into spatial evidence and evidential belief functions are estimated for the proposition that mineral deposits exist in a test area. The integrated maps of degrees of belief for the proposition that mineral deposits exist in a test area is classified into a binary mineral potential map. For the Baguio district (Philippines), the binary gold potential map delineates (a) about 74% of the training data (i.e., locations of large-scale gold deposits) and (b) about 64% of the validation data (i.e., locations of small-scale gold deposits). The results demonstrate the usefulness of a geologically constrained mineral potential mapping using data-driven evidential belief functions to guide further surficial exploration work in the search for yet undiscovered gold deposits in the Baguio district. The results also indicate the usefulness of evidential belief functions for mapping uncertainties in the geologically constrained integrated predictive model of gold potential.     

山东招掖金矿带内花岗岩与金矿化关系探讨

以花岗岩类及脉岩类的精确定年结果为基础,结合区内金矿床地质特征和近年来研究新进展,探讨了花岗岩类侵入与金矿化之间的空间、时间和成因关系。尽管区内花岗石类侵入体与金矿床间存在密切的窨及时间关系。但它们之间并不存在直接的成因联系,即这些金矿床并不是岩浆热液矿床。花岗石类侵入体和脉岩类的侵位通道和先存韧性剪切带是贯通深部流体的导矿构造,有利于深部成矿流体和上升和流体循环;花岗岩类与围岩的接触带及其内部断     

Quantitative estimation of the spatial distribution of geological objects and gold mineralization in the Degdekan-Arga-Yuryakh mineral district,Russian Northeast

An attempt was made to use GIS technologies for the development of methods of prognostic evaluation of the metal potential of a local territory based on mathematical statistics. The Degdekan-Arga-Yuryakh mineral district (Magadan region) was chosen as the research subject, where a spatial database of the geology and mineral resources was established. The application of methods of the spatial-statistical analysis of diverse cartographical-geological information provided the quantitative assessment of the spatial location of geological objects and gold mineralization in the region. Consequently, we were able to perform the spatial analysis of the location conditions of the gold deposits and recognize their relation to the geological characteristics. Based on the revealed geological features favorable for the location of mineralization, we distinguished two areas promising for commercial mineralization prospecting. Our work demonstrated the sufficient efficiency of the applied methods in large-scale metallogenic investigations at the ore cluster level.     

中国金矿矿产预测评价模型及资源潜力分析

在全国金矿资源潜力评价基础上,将全国金矿矿产评价模型总结为12类：与中深成侵入岩有关的热液型、破碎蚀变岩型、斑岩型、矽卡岩型、海相火山岩型、陆相火山岩型、微细浸染型、变碎屑岩地层中热液型、绿岩建造型、砂金型、风化壳型和砾岩型。其中,以与中深成侵入岩有关的热液型、破碎蚀变岩型、微细浸染型为主,其预测资源量约占总预测资源量的38%,21%和14%。根据资源量的空间分布及成矿地质背景划分了55个金矿成矿区带,通过对不同成矿区带对预测资源量、累计查明资源储量统计分析,金矿主要集中分布于胶东、华北地台南缘、西秦岭、东秦岭、辽东、滇黔桂、哀牢山成矿带等。根据金矿的成矿地质背景,结合金矿资源潜力及近年来金矿勘查进展,对下一步的工作部署提出参考建议。     

吉南老岭成矿带荒沟山、板庙子金矿床地质特征与成因

以吉林东南部老岭成矿带中较具规模的荒沟山、板庙子金矿床为代表,对矿床地质特征进行对比,认为区内太古界表壳岩、晚元古界老岭群为主要矿源层,北东向深大断裂带为主要控矿构造,空间上金矿体的分布与岩浆岩关系不密切。结合区内成矿地质条件及成矿物质来源分析,认为金矿床形成于中低温热液环境,深部流体、岩浆热液及大气降水作为成矿流体共同参与了成矿作用,以大气降水为主,构成大气降水—深源热液循环成矿系统。老岭金及多金属成矿带具有较大的成矿潜力和良好的找矿远景,区内金矿的分布主要与大型断裂带相关联的珍珠门组大理岩上部不整合有关。     

基于随机森林的四川省会理地区“拉拉式”铜矿成矿预测

四川省会理-会东矿集区是我国著名的铜资源基地。近年来,随着找矿勘查工作的深入,又提交了多处大中型铜矿床,表明该地区仍具有较大的找矿潜力。本文基于获取的地质、化探和物探数据,应用随机森林(Random Forest,RF)方法,在研究区开展"拉拉式"铜矿成矿潜力预测,取得了较好的效果:随机森林模型预测的平均袋外误差率为6. 25%,受试者工作特征曲线(Receiver Operating Characteristic Curve,ROC)的AUC值为0. 938。利用偏依赖图(Partial Dependence Plot,PDP)分析解释了预测变量与已知矿床(点)的响应关系,按平均精度下降法排序预测要素的重要性,对"拉拉式"矿床的找矿预测工作具有重要意义的前4个变量依次为:Cu元素含量,中-晚元古代(超)基性岩体临近度,Ni元素含量和PC2因子得分。从成矿地质条件角度分析,河口群地层无疑是"拉拉式"铜矿的重要找矿预测要素,但在随机森林模型中的重要性排序相对靠后。究其原因,一方面是与其它连续数值型预测要素不同,河口群地层是二值(0～1)变量;另外,河口群地层的分布范围受覆盖层的影响较大。根据随机森林模型生成的拉拉地区成矿有利度信息,圈定了6处找矿远景区。红铜山-落凼-红泥坡-姜驿高成矿有利度区带呈北北东向展布,主体上与研究区内重要的地质-地球化学-地球物理预测要素异常空间分布一致;其中蒿枝坝-落凼-红泥坡-姑鲁迷找矿远景区是本区已探明铜矿的主要分布区,其内还有进一步勘探的潜力;同时,该异常区呈半环形态,结合地质勘探揭示的变质火山岩厚度分布,及其西部受一组后期北北东向走滑断裂限制的特点,显示出古火山活动中心在西部,并可能存在被切割分离的另一半环异常,这为该地区后续地质研究和铜矿勘查指明了方向。     

中国金矿成矿地质特征、预测模型及资源潜力

为了摸清全国金矿资源潜力,科学合理地部署金矿地质勘查工作,在全国金矿资源潜力评价成果的基础上,总结了金矿成矿规律、时空分布及资源潜力特征,跟踪金矿勘查进展,提出金矿勘查部署建议。中国金矿床虽以小型居多,但大中型金矿床的资源储量约占80%。金矿床在中生代呈大规模成矿特征,其矿床数和资源储量均居主要地位,其次为新生代、晚古生代、中新元古代、早古生代。金矿床在空间上呈区域集中分布特征,根据成矿地质背景、成矿条件和金矿床空间分布,结合地球物理、地球化学特征、预测资源量,修订了金矿成矿区带划分方案,确定了57个Ⅲ级金矿成矿区带,其中胶东、小秦岭-伏牛山、滇黔桂、西秦岭、燕辽、松潘-摩天岭、东秦岭、长江中下游、丽江-哀牢山和吉南-辽东成矿区带,其查明资源储量和预测资源量在全国均居前列。以服务于矿产资源潜力评价为目的,提出了金矿预测类型划分方案,将金矿床类型归纳为12类,分别为与中深成侵入岩有关的热液型、微细浸染型、构造破碎蚀变岩型、陆相火山岩型、变质碎屑岩地层中热液型、斑岩型、夕卡岩型、砂金型、花岗绿岩型、海相火山岩型、风化壳型、砾岩型,其中以前5种矿产预测类型为主。在总结金矿床地质背景、地质特征和找矿标志的基础上,建立主要类型金矿预测评价模型。全国金矿资源潜力评价预测金资源量31 125.6 t,预测深度大多小于1 000 m,50%的预测资源量分布于已知矿床外围及深部。根据资源潜力评价成果,结合近年来金矿勘查取得新的找矿进展,找矿主攻矿床类型为中深成侵入岩有关的热液型、微细浸染型、构造破碎蚀变岩型、陆相火山岩型;中国东部胶东、小秦岭-伏牛山、西秦岭、滇黔桂为金矿重点勘查区带,已知矿床深部和外围仍是金矿重点找矿地段;西部地区如东昆仑、巴颜喀拉、冈底斯、班公湖-怒江、丽江-哀牢山等区带的金矿勘查突破,基础性地质勘查和科研工作投入,为西部地区金矿勘查开发提供理论和技术支撑,有利于开创西部地区金矿勘查的新局面。     

火山岩地区金矿的蚀变分带和成矿物理化学条件──成矿热流体与控矿环境相互作用过程的四维记录

本文主要讨论火山岩、次火山岩和相应侵入岩地区各类金矿的蚀变分带和形成条件，作者把成矿系统分为成矿热流体体系和控矿环境两个组成部分。热流体体系分成近地表和高侵位的两种类型，控矿系统分为火山中心控矿系统、高侵位岩体控矿系统和有区域性断裂系统复合的上述控矿系统。与近地表岩浆热流体体系有关的浅成热液金矿可分为低硫、高硫和富碲３个类型，与高侵位岩浆热流体体系有关的有斑岩型和浅成侵入体型。全面分析了与两种热流体体系有关的各类金矿产出的的地质环境、蚀变矿物组合的时、空分布，及其形成的地质和物理化学条件。提出了成矿热流体体系与控矿环境相互作用和进行物质能量交换过程的四维记录的新观点。     

柬埔寨王国磅通省三丹县金矿成矿地质条件分析

柬埔寨王国磅通省三丹县地区的整体地质工作程度较低,对该地区已有金矿床（点）成矿地质条件的研究对于该区域金矿勘查具有重要意义。本文详细阐述了三丹县金矿床（化）的成矿地质要素,并与IRGS型金矿进行了对比研究,认为陆缘弧和弧后克拉通盆地接触部位的大地构造背景和钙碱性区域岩浆岩条件,为区内金矿化提供了有利的区域地质条件,这与典型IRGS型金矿床具有相似的构造背景。调查区内的金矿体（矿化）常发育在侵入岩及其边缘地带,在空间分布上金矿化与侵入岩关系密切,且围岩常具石英-碳酸盐-绢云母化围岩蚀变组合,金矿石以网脉状和角砾状类型为主,这符合IRGS型金矿的矿化特征。初步认为区域内金矿化与侵入岩关系密切,属于IRGS型金矿。     

Three-dimensional mineral prospectivity modeling for targeting of concealed mineralization within the Zhonggu iron orefield,Ningwu Basin,China

The Zhonggu iron orefield is one of the most important iron orefields in China, and is located in the south of the Ningwu volcanic basin, within the middle and lower Yangtze metallogenic belt of eastern China. Here, we present the results of new 3D prospectivity modeling that enabled the delineation of areas prospective for exploration of concealed and deep-seated Baixiangshan-type mineralization and Yangzhuang-type mineralization within the Zhonggu orefield; both of these deposits are Kiruna-type Fe-apatite deposits but are hosted by different formations within the Ningwu Basin. The modeling approach used during this study involves 3 steps: (1) combining available geological and geophysical data to construct 3D geological models; (2) generation of 3D predictive maps from these 3D geological models using 3D spatial analysis and 3D geophysical methods; (3) combining all of the 3D predictive maps using logistic regression to create a prospectivity map. This approach integrates a large amount of available geoscientific data using 3D methods, including 3D geological modeling, 3D/2D geophysical methods, and 3D spatial analysis and data integration methods. The resulting prospectivity model clearly identifies highly prospective areas that not only include areas of known mineralization but also a number of favorable targets for future mineral exploration. The 3D prospectivity modeling approach showcased within this study provides an efficient way to identify camp-scale concealed and deep-seated exploration targets and can easily be adapted for regional- and deposit- scale targeting.     

Application of Spectral Angle Mapper Classification to Discriminate Hydrothermal Alteration in Southwest Birjand,Iran, Using Advanced Spaceborne Thermal Emission and Reflection Radiometer Image Processing

The purpose of this study is to evaluate the Spectral Angle Mapper (SAM) classification method for determining the optimum threshold (maximum spectral angle) to unveil the hydrothermal mineral assemblages related to mineral deposits. The study area indicates good potential for Cu-Au porphyry, epithermal gold deposits and hydrothermal alteration well developed in arid and semiarid climates, which makes this region significant for Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image processing analysis. Given that achieving an acceptable mineral mapping requires knowing the alteration patterns, petrochemistry and petrogenesis of the igneous rocks while considering the effect of weathering, overprinting of supergene alteration, overprinting of hypogene alteration and host rock spectral mixing, SAM classification was implemented for argillic, sericitic, propylitic, alunitization, silicification and iron oxide zones of six previously known mineral deposits: Maherabad, a Cu-Au porphyry system; Sheikhabad, an upper part of Cu-Au porphyry system; Khoonik, an Intrusion related Au system; Barmazid, a low sulfidation epithermal system; Khopik, a Cu-Au porphyry system; and Hanish, an epithermal Au system. Thus, the investigation showed that although the whole alteration zones are affected by mixing, it is also possible to produce a favorable hydrothermal mineral map by such complementary data as petrology, petrochemistry and alteration patterns.     

Using Remote Sensing Data to Delineate the Lineaments for Hydrothermal Mineral Prediction in Heqing Area, Northwest Yunnan Province, China

Lineament extraction and analysis is one of the routine work in mapping medium and large areas using remote sensing data, most of which are satellite images. Landsat Enhanced Thematic Mapper （ETM） of 945×1 232 pixels subscene acquired on 21 March 2000 covering the northwestern part of Yunnan Province has been digitally processed using ER Mapper software. This article aims to produce lineament density map that predicts favorable zones for hydrothermal mineral occurrences and quantify spatial associations between the known hydrothermal mineral deposits. In the process of lineament extraction a number of image processing techniques were applied. The extracted lineaments were imported into MapGIS software and a suitable grid of 100 m×100 m was chosen. The Kriging method was used to create the lineament density map of the area. The results show that remote sensing data could be useful to extract the lineaments in the area. These lineaments are closely correlated with the faults obtained through other geological investigation methods. On comparing with field data the lineament-density map identifies two important high prospective zones, where large-scale deposits are already existing. In addition the map highlights unrecognized target areas that require follow up investigation.     

Porphyry copper potential mapping using the weights of evidence model in a GIS,northern Shahr e Babak,Iran

A variety of spatial geological data were compiled, evaluated and integrated to produce a potential map for porphyry copper deposits in the northern Shahr e Babak, Iran, within a total area of approximately 408 km². Remotely sensed data including LANDSAT Thematic Mapper were used to create the hydrothermal alteration haloes around intrusive bodies. Geological data, such as exposed granitic to intermediate intrusions, and part of the lineaments were extracted from available geological maps. Aeromagnetic data were also used to extract magnetic anomalies and extra lineaments. The Conditional Independence test was carried out on five binary maps representing diagnostic deposit recognition criteria, and four of them were then integrated using a weights of evidence model. The procedure generated a posterior probability map identifying favourable areas for porphyry copper deposits. The final map highlights the most important known copper deposits in high favourability domains. Some new target areas are also located in the favourability map and warrant further investigation.     

华北克拉通北缘及邻区印支期岩浆活动与钼和金成矿作用

对华北克拉通北缘及邻区19处钼矿床和5处金矿床的产出环境、形成时代和成矿机理及其与印支期侵入岩的关系进行了讨论。尽管各个矿床所处的地理位置不同,但是它们大都在前寒武纪或早古生代地层中产出,并且与印支期侵入岩具有密切的时空分布关系。印支期钼矿床的形成作用可以从早三叠世一直持续到晚三叠世,大规模成矿作用高峰期为230~220 Ma。相比之下,金矿床的形成时间明显早于钼矿床,同位素年龄数据集中分布在245~239 Ma。研究结果表明,自早三叠世开始,华北克拉通北缘及邻区曾发生过多期大规模伸展构造作用,并且形成若干条近东西向展布的裂陷带。张裂构造作用所诱发的富碱性岩浆作用及相关流体活动为钼或金矿床的形成提供了动力和物质来源,因此,印支期侵入岩发育区是寻找隐伏钼或金矿床的有利地区。     

南秦岭汉阴北部金矿田长沟金矿区控矿构造解析

南秦岭汉阴北部金矿田含矿岩系主要是志留系梅子垭岩组中浅变质岩层，该套地层经历了中生代的构造变形，复杂多样，其中发育的脆-韧性剪切带成为梅子垭岩组发育蚀变岩型金矿富集的良好场所。通过对汉阴北部金矿田近年新发现的长沟金矿区及周邻区带成矿地质背景、控矿构造特征等进行解析研究，结合以往资料，总结汉阴北部金矿田该类型金矿床的控矿构造特征和成矿规律，初步探讨长沟金矿床的热液成因类型。研究发现汉阴北部金矿田区发育有五条脆-韧性剪切带，其构造样式、变质作用具多样性和多期性，其中第二期变形与金成矿作用关系密切；长沟金矿区受区域DSZ3(≈RF5)脆-韧性剪切带及多期构造置换中的S₂面理控制，控矿构造样式具有斜列排布特征。含矿流体包裹体研究认为其在低—中温热液环境形成，主要是在退变质作用下易于在局部两种岩性差异界面附近、片理面之间薄弱变形带、密集剪切节理带或劈理化带等有利构造部位含金热液发生富集成矿。因此，脆-韧性剪切带及其多期面理置换与密集片理、剪切节理带及热液蚀变岩是主要的控矿构造类型。进一步的找矿预测工作主要应该紧抓其脆-韧性剪切带的走向延伸和倾向延深，更应重视侧向斜列富集规律。      

桂东大瑶山成矿带古木口金矿床地质特征及找矿方向

古木口金矿是在桂东大瑶山成矿带上发现的首例中型规模以上高品位金矿,其矿床类型属于中低温岩浆热液型。该金矿矿体呈似层状、脉状、透镜状产出,受断裂、成矿结构面及构造蚀变带控制,矿床在垂向和横向上具有石英脉型、破碎蚀变岩型及斑岩型分带特征。为及时总结矿区勘查新成果,推动该区找矿新突破,研究矿体与寒武系含碳细碎屑岩系、层间引张型走滑转换断裂、花岗闪长斑岩组合要素的空间关系,以及近矿围岩蚀变矿物组合标志、土壤化探异常等成矿综合信息;运用土壤地球化学测量及异常带槽探、钻探揭露等综合找矿方法,在总结分析了矿区地质-地球化学特征及矿化时空分布规律的基础上,提出了该区带的找矿方向。结果显示,该矿区深部及外围具有较好的找矿前景,特别是北西向断裂、引张型走滑转换断裂、伸展型脆-韧性剪切异常带利于寻找破碎带蚀变岩型富金矿,其构造相对封闭环境的深部是寻找斑岩型金矿的有利地段。     

新疆西南天山金矿床主要类型、特征及成矿作用

文章在总结前人研究成果的基础上,综合论述了西南天山金矿的成矿地质背景、金矿床的时空分布和基本特征。根据矿床地质特征和控矿因素,将西南天山的金矿划分为与剪切带有关的金矿床、与侵入岩有关的金矿床(包括斑岩型)、石英-重晶石脉型金矿床、与火山岩有关的金矿床和矽卡岩型金矿床5类,其中与剪切带有关的金矿床是最重要的矿床类型。探讨了西南天山金矿的成矿时代、成矿物质和成矿流体来源,以及成矿地球动力学机制。提出与剪切带有关的金矿床成矿物质主要来源于岩浆和海相碳酸盐岩,成矿流体主要来源于岩浆水或主要来自大气降水,混合少量岩浆水。石英-重晶石脉型金矿床成矿物质来自容矿地层,成矿流体主要来源于沉积建造水。与剪切带有关的金矿、与侵入岩有关的金矿、石英重晶石脉型金矿和矽卡岩型金矿成矿时代主要集中在二叠纪—三叠纪,形成于后碰撞构造演化阶段。斑岩型和浅成低温热液型金矿床形成于岛弧挤压环境。     

甘肃北山花岗岩与金矿成矿作用

甘肃北山地区是一重要的金矿化集中区,具较大的金资源潜力。由于勘查和研究程度低,尚未取得找矿突破。本文从金矿的空间分布、金矿床的地质特征、花岗岩的时空分布、金矿与花岗岩的时空关系和矿床的稳定同位素特征等的研究,探讨了本区金矿成矿作用与花岗岩类侵入活动的关系。研究该区花岗岩类的时空演化及其与金成矿作用的关系的研究,对于寻找...     

From 2D to 3D: Prospectivity modelling in the Taupo Volcanic Zone,New Zealand

A 2D prospectivity model of epithermal gold mineralisation has been completed over the Taupo Volcanic Zone (TVZ), using the weights of evidence modelling technique. This study was used to restrict a 3D geological interpretation and prospectivity model for the Ohakuri region. The TVZ is commonly thought of as a present-day analogue of the environment in which many epithermal ore deposits, such as in the Hauraki Goldfield, Coromandel Volcanic Zone, are formed. The models utilise compiled digital data including historical exploration data, geological data from the Institute of Geological and Nuclear Sciences Ltd. Quarter Million Mapping Programme, recent Glass Earth geophysics data and historic exploration geochemical data, including rock-chip and stream sediment information. Spatial correlations between known deposits and predictive maps are determined from the available data, which represent each component of the currently accepted mineral system model for epithermal gold. The 2D prospectivity model confirms that the TVZ has potential for gold mineralisation. However, one of the weaknesses of this weights of evidence model is that the studies are carried out in 2D, with an approximation of 3D provided by geophysical and drilling data projected to a 2D plane. Consequently, a 3D prospectivity model was completed over the Ohakuri area, constrained by the results of the 2D model and predictive maps. The 3D model improved the results allowing more effective exploration targeting. However, the study also highlighted the main issues that need to be resolved before 3D prospectivity modelling becomes standard practise in the mineral exploration industry. The study also helped develop a work flow that incorporates preliminary 2D spatial data analysis from the weights of evidence technique to more effectively restrict and develop 3D predictive map interpretation and development.