【作者】 李智明；

【导师】 薛春纪；

【作者基本信息】 长安大学 ， 地质工程， 2007， 博士

【摘要】 从矿床成矿理论研究方面看,边缘成矿是近年来研究的重点课题。大陆边缘是成矿作用最显著的地带之一,世界上很多矿集区和大型、超大型矿床都分布在大陆边缘。目前已发现的MVT型铅锌矿床在北美典型发育于大型前陆盆地的边缘,VMS型和SEDEX型也都发育在大陆的边缘地带。大陆边缘深浅部沟通、流体汇聚、矿源丰富、热动力异常、长期活动、成矿潜力巨大,因此,大陆边缘铅锌成矿作用与成矿规律的研究对于丰富成矿学理论,具有十分重要的意义。大陆边缘流体地质过程是成矿作用研究的核心,也是指导找矿的关键。从矿床定位预测与资源勘查方面看,随着找矿主体对象由地表矿、浅部矿、易识别矿向隐伏矿、深部矿、难识别矿的逐渐转变,矿床定位预测工作已成为当前区域成矿学与成矿预测学领域的前沿和热点。近20年来,国际上金属矿产找矿勘查方面的重大突破主要集中在现有大型矿山的外围和深部,以及重要成矿带的矿集区或地质工作程度极低地区;另一特征是矿床类型主要集中在以火山岩为主岩和以沉积岩为主岩的类型上,斑岩型矿床也是一个重要类型。据统计,以火山岩为主岩和以沉积岩为主岩的矿床是近十年来发现最重要的矿床类型。以沉积岩为主岩的密西西比河谷型（MVT）和沉积喷流型（SEDEX或称热水沉积）是当前富铅锌矿的代表类型。就世界查明的资源储量与开采产量而言,以沉积岩为主岩的铅锌矿床类型可占Pb、Zn总储量与产量的1/2到2/3;由此可见,沉积岩容矿型Pb、Zn矿是今后一段时期内找矿的主攻类型和找矿方向。扬子北缘及周边地区成矿条件非常优越,分布着丰富的铅、锌矿产资源,主要为海底喷流沉积（SEDEX）型铅锌矿床和MVT型铅锌矿床,新近又发现了马元铅锌矿田、镇旬志留系铅锌矿田、湖北神农架冰洞山震旦系铅锌矿床、湖北神农架沐浴河铅锌矿床等一大批铅锌矿床,在扬子北缘及周边地区从震旦系到二叠系地层中巨大的成矿和找矿潜力已初现端倪。从目前扬子北缘及周边地区所发现的铅锌矿床看,成矿时代、赋存层位、矿床成因具有较为明显的层控特征:西秦岭地区的柞水泥盆纪盆地中主要发现的是海底喷流沉积（SEDEX）型铅锌矿,且有后期构造热事件的改造作用;往东的镇（镇安）—旬（旬阳）地区志留系铅锌矿具有喷流沉积—改造的特点;陕南地区的南郑县马元铅锌矿田一直东延至鄂西地区的铅锌矿具有MVT型成矿系列的特点;并且矿床受改造的程度有显著变化,马元楠木树铅锌矿为强改造型,神农架冰洞山铅锌矿为弱改造型。其成矿作用与成矿规律的研究一直备受关注,但MVT和SEDEX型铅锌矿床彼此之间的关系如何?扬子北缘MVT矿床与典型MVT矿床的差异及特点是什么?该区铅锌矿床的成矿控制要素和找矿最有效标志是什么?找矿方向是什么?都需要进一步深入的研究,以便促进该区乃至国内外与该区成矿条件相同或类似地区的找矿实践。本项研究以新的成矿理论为指导,以沉积盆地和大陆边缘等区域构造研究为主线,以矿床地质特征为基础,以综合信息量法和人工神经网络模型预测法为手段,对扬子北缘及周边地区铅锌矿床的成矿地质背景、成矿因素、成矿地质条件、找矿方向进行了系统的总结和研究。扬子北缘以及周边地区已发现的铅锌矿床,分别产于不同的构造背景和地质环境,但具有相同的物质来源方式,形成不同规模的层控型矿床。震旦纪和志留系与碳酸盐岩有关的成矿系统在本区是主要的,同时都遭遇了不同的后期改造。该区铅锌矿床是在板块的张裂期→平稳过渡期→挤压收缩期形成的。在震旦纪,扬子北缘处于稳定陆缘台坪环境,热基底产生了大规模的热水循环成矿系统,形成了范围大、层位稳定的低温热液充填型（MVT）矿床。在扬子板块北部被动大陆边缘（镇旬）,早古生代构造上具有稳定及半稳定性质,发育复理石沉积建造,形成喷流沉积型（SEDEX）矿床。扬子北缘的马元铅锌矿田产于震旦纪未受变质的白云岩中;含矿岩石为角砾状白云岩,具层控、岩控的特点;成矿温度为85～210℃,具有低温—超低温特征;富含有机质的热卤水,常伴生有沥青,气相包裹体中有CH₄;盐度为7.6～12.0wt.,含H₂S、CO₂;矿石中δ³⁴S范围为8‰～33.48‰,平均18.28‰,有富集重硫的特征,不具有塔式分布特征,主要来源于台地潮坪环境;普通铅同位素具有壳幔混合来源的特征,模式年龄为4.20～6.37亿年,大体和震旦系形成时代相同,其特征类似于MVT型铅锌矿。镇旬地区的铅锌矿床分布于志留纪地层中,矿体以层状、似层状产出;成矿温度为130℃～250℃,具有中低温特征;气相成分以H₂O（气）占绝对优势,CO₂的含量也占相当的比例,CH₄稀少,总体表现为H₂O＞CO₂＞N₂＞CO＞CH₄＞H₂＞O₂的特点;镇旬地区志留系中铅锌矿的硫同位素全部为正值,δ³⁴S为2.38～10.46‰,主要来源于海水;矿石铅具有壳幔混合来源的特点,源区年龄老于成矿年龄;镇旬矿田志留系铅锌矿床在矿体产出方式、矿石构造以及铅同位素组成、成矿温度、包裹体水氢、氧同位素组成和稀土元素组成等方面与国外热水喷流沉积型铅锌矿床相比较均相似或一致,确认镇旬志留系铅锌矿为海底热水喷流沉积成因。扬子北缘及周边地区铅锌矿矿床类型主要为MVT型和SEDEX型,热基础和沉积环境是形成矿床的两大要素,稳定陆缘台坪和张裂潮坪环境是成矿的必要条件,陆地周边及隆起边缘、盆地与盆地的边缘等对成矿有控制作用。这两类矿床成矿过程的共同点是MVT型矿床的“热基底”、SEDEX型矿床的“地幔热点”背景等构成“热基础”;构造环境常是大型盆地边缘或盆地内隆起边部;含矿热水的形成都是来自地层中沉积物中排放出来的溶液,在加热形式、萃取矿质来源、运移方式等方面均具相同性;两者的容矿围岩基本上都为碳酸盐岩岩系,层控特征十分明显;受后期构造影响,都存在不同程度的改造。其不同点为两种含矿热水的运移通道不同,导致矿床定位不同。本文利用综合信息量法和BP人工神经网络模型预测法,建立了找矿有利度模型,在定量的数值计算的基础上,划分出了七个找矿远景区,使找矿目的性更明确,指出了镇旬矿田和马元矿田更具目标性的找矿远景区和找矿方向。更多还原

【Abstract】 The metallogenic theory of marginal metallogenesis has become one of the most important research projects during recent years. Many ore deposit concentrated districts, large and super-large deposits were distributed along the continental margin, in which the metallogenesis were remarkable. The MVT type zinc-lead deposits found in the North America were typically distributed along the margin of large forelandbasin, and so were the VMS and SEDEX type zinc-lead deposits. The research on zinc-lead metallogenesis of the continental margin are very important, because of the abound ore resources, long-time activity, huge metallogenic potential, and so on. The core of the research on metallogenesis are the fluid and geological process of the continental margin, which are also the key of prospecting.The position and forecast of the ore deposits are the hotspot and front of Regional Metallogeny and Mineral Prediction at present, with the changing of prospecting objects from surface, shallow, recognizable deposits to concealed, deep, difficultly recognizable deposits. During the last 20 years, the major breakthrough on the prospecting of metal mineral resources in the world are mainly in the peripheral and deep area of the large deposit, important ore deposit concentrated districts or the district with less geological work. In addition, the major types of the deposits are mainly the types that the host rocks are volcanic rocks and sedimentary rocks during the last 10 years, and so are the porphyric deposits. The MVT and SEDEX type zinc-lead deposits are the most iomportant zinc-lead deposits all over the world now, and the Zn-Pb reserves of the deposits whose host rocks are sedimentary rocks are more than half of the world’s Zn-Pb reserves. So, the prospecting directions are mainly the deposits whose host rocks are sedimentary rocks in future.Abundant lead-zinc mineral resources were distributed in the northern margin and surrounding area of the Yangtze Platform, whose types were mainly MVT and SEDEX type, and the newest zinc-lead deposits discovered were Mayuan, Zhenxun, Shennongjia bingdongshan and Muyuhe zinc-lead deposits. Ore deposits discovered in the area up to now are obviously characterized by their mineralization age, ore host strata and origin of ore deposit etc. For example, SEDEX lead zinc deposits are mainly occurred in the Zhenxun basin in the southern Qinling area and mostly reformed by later heat structural events. The lead-zinc deposits of Mayuan, southern area of Shanxi eastern-word to the western area of Hubei province are characterized by MVT mineralization series with obviously strong reformation type of lead-zinc deposits in Nanmushu, Mayuan nanmushu, and weak reformation type of lead-zinc deposits in Bingdongshan, Shennongjia. But there are many problems which need more research, such as the relationship between MVT and SEDEX zinc-lead deposits, the difference and characteristics of the MVT zinc-lead deposits in the northern margin of the Yangtze Platform and the typical MVT zinc-lead deposits, the ore-controlling factors and prospecting targets of the Zn-Pb deposits in the area, the prospecting direction, and so on.With the comprehensive data method and BP prediction method, this research systematically summarize the geological setting, ore-controlling factors, ore-forming conditions and prospecting targets based on the basic geological characteristics, taking the regional structure, sedimentary basins and mainland edge as the main research line.Lead and zinc deposits discovered in the northern margin and surrounding area of the Yangtze Platform separately occur in different structural setting with different scale, same material resources, forming different sizes of strata bound ore deposits. The mineralization system related to carbonate rocks in Sinian period and Silurian period is the main ore forming system, also suffering different later reformation. The lead and zinc ore deposits were formed in the extending period→the steady transition period→press and constringency period. The northern margin of the Yangtze Platform is placed in a platform flat setting of a stable continental margin. Large scale of thermal cycle ore forming system occurs in the ancient volcanic arc "heat basement". Mineralization is charactered by large scope, stable layer, hydrothermal filling rich in organic. Origin type of ore deposits is basically the same to the MVT. Ore deposits in Zhenan—Xunyang area are located in the passive continental margin of the Yangtze plate, i.e. the southern Zhen—Xun Paleozoic sedimentary basin. Where is tectonically charactered by stable and semi-stable natures, developed by various type of stable——semi-active sedimentary formations, and SEDEX deposits formed.The Mayuan lead-zinc ore field in the Yangtze platform occurs in carboniferous rock, and its host rock is unmetamorphosed dolomite. The ore bearing rock is breccia form dolomite controlled by strata and magma rock. The ore-forming temperature is from 85 to 210℃, which is low to ultra-low. It contains organic hot brine, accompanied by crystalline asphalt. CH₄, H₂S and CO₂ are contained in the inclusions, whose salinity is 7.6-12.0 wt. Sulphur in the ores is from sea water, and the dating by Pb isotope is 420-637 Ma, generally similar to the age of Sinian. In a word, it is similar to the MVT lead zinc deposit, compared with their characters in geology, isotope, REE and trace element.The Zhenxun Zn-Pb deposit is distributed in the strata of Silurian period, whose ore bodies is layered or like-layered. The ore-forming temperature is from 130 to 250℃, which is low to middle-low. There are lots of H₂O and CO₂, with less CH₄. The values of sulphur isotpe are all passive, and sulphur in the ores is mainly from sea water. The Pb isotope show that lead in the ores is from both the crust and mantle. The lead zinc deposits in Zhenxun ore field in Silurian is similar or consistent with the SEDEX lead zinc deposit from their occurrence of ores, ore texture, Pb isotope composition, REE composition, ore forming temperature and H-0 isotope composition of the inclusions. Therefore, the Zhenxun lead-zinc deposit is confirmed to be SEDEX deposit.The mineralization process for lead and zinc deposits discovered in the northern margin and surrounding area of the Yangtze Platform shows similarity and difference. "Heat basement"+ sedimentary are the two factors for forming the deposit. Stable platform flat and tension tidal flat on continental margin are the essential condition for the mineralization. "Heat basement" was composed of "mantle plume" of SEDEX deposit and "heat basement" of MVT deposit. The tectonic setting is normally the margin of large basin or uplift edge inside basin. Mineralized hydrothermal liquid is from the solution in sediments of strata. It shows similarity in heating form, extraction of mineral resource and transfer way etc. The host rocks in both of them are carbonate rocks, showing obvious characteristics of strata bound. The deposits were in a certain degree reformed, because of the later tectonism. The difference is the transfer path of the both mineralization hydrothermal liquid which resulted in the difference location of deposits.A vantage degree model is established for ore prospecting by using the comprehensive data method and BP prediction method. Seven prospecting targets are ascertained on the basis of quantitative calculation, which makes the intention more clearly in Zhenxun ore field and Mayuan ore field.更多还原