An SVM-based machine learning method for the separation of alteration zones in Sungun porphyry copper deposit

Sungun porphyry copper deposit is in East Azarbaijan province, NW of Iran. There exist four hypogene alteration types in Sungun: potassic, propylitic, potassic–phyllic, and phyllic. Copper mineralization is essentially associated more with the potassic and less with the phyllic alterations and their separation is, therefore, quite important. This research has tried to separate these two alteration zones in Sungun porphyry copper deposit using the Support Vector Machine (SVM) method based on the fluid inclusion data, and seven variables including homogenization temperatures, salinity, pressure, depth, density and the Cu grade have been measured and calculated for each separate sample. To apply this method, use is made of the radial basis function (RBF) as the kernel function. The best values for λ and C (the most important SVM parameters) that perform well in the training and test data are 0.0001 and 1, respectively. If these values for λ and C are applied, the phyllic and potassic alteration zones in the training and test data will be separated with an accuracy of about 95% and 100%, respectively. This method can help geochemists in separating the alteration zones because classifying and separating samples microscopically is not only very hard, but also quite time and money consuming.     

台湾峡谷中段沉积特征及流体机制探讨

海底峡谷、高弯度水道等深水沉积单元中的流体活动方式是人们关注的热点.本次研究利用高分辨地震资料,结合地形地貌特征对台湾峡谷中段的沉积特征及流体活动方式进行初步探讨.台湾峡谷中段发育内堤岸(inner levee),它成层性好、地层产状倾斜,地震反射特征与峡谷西岸和下覆滑塌体明显不同,内部结构表现为逐级上超的特征,以侧向加积为主.曲流河和深水高弯度水道的点坝均发育于河(水)道拐弯处,由于离心力作用,沉积物在凸岸堆积形成点坝.该内堤岸位于峡谷中段直线型地段,不具备形成点坝的地形地貌条件,综合分析认为该内堤岸是由垂直于峡谷轴向、自西向东的底流与沿峡谷向下的重力流交互作用形成的.     

新疆白杨河大型铍铀矿床成矿流体特征及矿床成因初探

新疆和布克赛尔县白杨河大型铍铀矿床是亚洲最大的铍矿床,其矿体产出于晚石炭世微晶花岗斑岩与上泥盆统塔尔巴哈台组(D3t)中酸性火山岩的接触带上,该矿床为典型的热液矿床.萤石作为白杨河铍铀矿床中与成矿作用密切相关的脉石矿物,发育大量气液包裹体.通过对萤石中流体包裹体的显微测温,获得了其主成矿期包裹体的均一温度,为237～372℃(n=40),平均为308.5℃,反映该矿床为中高温热液矿床.萤石以相对富集中稀土(MREE) ((La/Yb)N=3.18～3.55),强烈亏损Eu (δEu=0.01),REE分布模式呈“V”字型为特征.萤石锶钕同位素数据显示出较高的锶同位素初始比值(0.7106),以及正εNd(t)值(3.50～2.95),相似于微晶花岗斑岩的锶钕同位素组成((87Sr/86Sr)i=0.7143～0.7466,εNd(t)=4.06～5.29),由此提出成矿流体主要来自微晶花岗斑岩岩浆分异的晚期热液.主成矿期的萤石包裹体显示高温、低盐度的特征,推断成矿流体源于微晶花岗斑岩晚期岩浆热液与大气降水的混合.     

Granite ages within the Archaean Pilbara Block,Western Australia

Within the Pilbara Block of Western Australia, a complex of migmatite, gneissic and foliated granite near Marble Bar is intruded by a stock of younger massive granite (the Moolyella Granite) with which swarms of tin‐bearing pegmatites are associated. The age of the older granite has been determined by the Rb‐Sr method as 3,125 ± 366 m.y., and that of the Moolyella Granite as 2,670 ± 95 m.y. Initial Sr⁸⁷/Sr⁸⁶ ratios suggest that the older granite is close to primary crustal material, but that the Moolyella Granite consists of reworked material. It probably formed by partial remelting of the older granite.     

The origin of tin deposits in the Mount Wells region,Pine Creek Geosyncline,Northern Territory

Tabular steeply dipping cassiterite‐bearing lodes in the Mount Wells region are hosted by lower greenschist fades metasediment of the Pine Creek Geosyncline within the contact aureole of late orogenic granitoids. The latter are predominantly I‐type, but S‐type phases are developed near the sediment‐granitoid contact.

Quartz, cassiterite, pyrite, arsenopyrite, chalcopyrite and pyrrhotite are the main minerals. Two types of lodes are present: (i) Sn‐quartz lodes containing 5–10 vol% sulphide minerals; and (ii) Sn‐sulphide lodes containing ～ 70 vol% sulphide minerals. At the surface, the former appear as normal quartz veins and the latter as hematite‐quartz breccia resulting from the collapse of original sulphide‐rich lodes as a consequence of volume reduction due to oxidation and leaching.

Two stages of quartz veining are recognized in both types of lodes. Cassiterite is present in stage I while stage II is composed of barren quartz with minor pyrite. Late stage III carbonate veinlets are present in Sn‐sulphide lodes. The lode‐wallrock contact is sharp with weak alteration effects confined to the fringe of the lodes. The alteration minerals include sericite, quartz, tourmaline, chlorite, pyrite and minor K‐feldspar.

Four types of fluid inclusions are present in vein quartz and cassiterite: Type A (CO₂ ± H₂O ± CH₄); Type B (H₂O+～ 20% vapour); Type C (H₂O+ < 15% vapour) and Type D (H₂O+ < 15% vapour + NaCl). Early ‘primary’ inclusions represented by Types A and B are present in stage I only and have a well‐defined temperature mode at ～300°C and a salinity range of 1–20 wt% eq NaCl. Types C and D inclusions are ‘secondary’ in stage I and primary in stage II and have a temperature mode at 120–160°C and salinities from about 1 to more than 26 wt% eq NaCl. Variable H₂O‐CO₂ ratios of Type A inclusions and homogenization in CO₂ or H₂O phase at near identical temperature indicate entrapment at the H₂O‐CO₂ solvus and define a pressure of ～ 100 MPa. The melting sequence of frozen inclusions suggests that the ore fluids were mainly H₂O‐CO₂‐CH₄‐Na‐Ca‐Cl brines. This is also confirmed by Raman Laser Spectrometry.

Oxygen and sulphur isotope data are consistent with a magmatic origin of the ore fluids. The δD values are up to 20%0 higher than those expected for magmatic fluids and probably resulted from interaction of the latter with the carbonaceous strata. This interpretation is supported by δ¹³C data on the fluid inclusion CO₂.

Fluid inclusions, stable isotope and mineralogical data are used to approximate the physico‐chemical parameters of the ore fluids which are as follows: T 300°C, m Cl～2, fO₂ ～ 10^‐35, mSS ～ 0.01, Sn ～ 1 ppm, Cu ～ 1 ppm and pH ～ 5.5.

It is suggested that fluids of granitic parentage interacted with the enclosing sediment and picked up CO₂, CH₄ and possibly Ca. The granitic phases became reduced due to this interaction and developed S‐type characteristics. Tin was probably partitioned into the CH₄‐bearing reduced fluids. At some stage the fluid overpressure exceeded the lithostatic lode enforcing failure of the carapace and the intruded rocks by hydraulic fracturing causing CH₄ and CO₂ loss resulting in the precipitation of the ore minerals.     

Skarn development from limestone adjacent to the Glenrock Granodiorite,Marulan Batholith,New South Wales,Australia

Skarns are developed over two temperature‐time intervals in calcite limestone adjacent to the southern extension of the Glenrock Granodiorite, a pluton of the Marulan Batholith, Southern Highlands, New South Wales. The initial volumetrically‐dominant prograde phase of skarn formation produced a suite comprising bimetasomatic skarn, including pyroxene endoskarn, potassic endoskarn and wollastonite‐bearing exoskarn, together with mineralogically‐zoned vein skarn, massive garnet‐pyroxene skarn and calcite‐vesuvianite skarn. Retrograde replacement is manifested by the development of hydrous silicate minerals, carbonate and cross‐cutting sulphide veinlets.

A genetic model is proposed to account for the development of bimetasomatic skarn in the deposit. Exoskarn geochemistry indicates addition of many components relative to an essentially pure limestone precursor, including Si, Al, Fe, Zr, Zn, S, Mn and Cu, negligible transfer of K, Na and Rb and loss of CO₂. Strontium and Ca loss from the parent limestone is indicated by mass balance calculations at constant volume.

Garnet and pyroxene compositions in the massive garnet‐pyroxene skarn range from Gr₃₀ to Gr₆₆ and Hd₆₁ to Hd₈₇, respectively. Compositions from Gr₆₇ to Gr₉₅ are typical of the vein skarn garnets. Chemical zonation patterns in garnet, pyroxene and vesuvianite are generally characterized by rim Fe depletion relative to cores of grains.

Prograde skarn probably formed at T = 500–580°C; P < 220 MPa. The massive garnet‐pyroxene skarn evolved under conditions of log fO₂ = ‐18.9 to ‐22.9 (assuming a constant fCO₂ of 20 MPa) within the fS₂ stability field of pyrrhotite. Retrograde skarn formed at T < 400°C, possibly under conditions of X_H2O < 0.01.

Vesuvianite plus wollastonite assemblages, present in exoskarn, probably attest to very water‐rich conditions. The marble wall rocks, isolated from the source of skarn‐forming fluids, probably evolved under conditions of minimum X_co2 >0.2. Low temperature CO₂ ‐rich fluid inclusions and prehnite (stable at X_co2 <0.01), present in the marble and skarn, respectively, suggest that substantial differences in X_co2: X_H2O were maintained during cooling.

Observed mineralogical and chemical zonation within the skarn reflects the complex interaction of T, P, fO₂, Xco₂ and other chemical variables such as a_SiO2 and a_Al2O3 throughout the skarn system. No single variable can account adequately for the mineralogical diversity observed in the skarn deposit.     

Mineralogical and Geochemical Constraints on the Genesis of the Carbonate‐Hosted Jebel Ghozlane Pb–Zn Deposit (Nappe Zone,Northern Tunisia)

The Pb–Zn deposit at Jebel Ghozlane, in the Nappe zone (northern Tunisia), is hosted by Triassic dolostones and Eocene limestones and is located along faults and a thrust‐sheet boundary. The sulfide mineralization of the deposit consists mainly of galena and sphalerite and occurs as vein, stockwork, breccia, dissemination and replacement ores. Three hydrothermal stages are involved in the formation of the ores: stage I is dominated by celestite‐barite, hydrothermal dolomite DII, colloform sphalerite, and galena I; stage II consist of galena II; and stage III contains calcite. Galena in the deposit yielded average ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of 18.705, 15.667 and 38.734, respectively, suggesting a single upper crustal source reservoir for metals. Trace element data indicate the presence of Zn‐ and As‐free galena and As‐rich galena (with 0.2–0.5% As). Sphalerite contains 0.4% As, 0.7–0.9% Cd and 0.1–1.5% Fe. Microthermometric analysis of fluid inclusions in celestite shows that the deposit formed from fluids composed of heterogeneous mixtures of saline (19.5 ± 1 wt% NaCl eq.) aqueous solutions sourced from basinal brines, and gaseous CO₂‐rich phases bearing low amounts of CH₄, N₂ and/or H₂S, at temperatures of 172 ± 5°C.     

Fluid inclusion evidence for hydrothermal fluid evolution in the Darreh-Zar porphyry copper deposit,Iran

The Darreh-Zar porphyry copper deposit is associated with a quartz monzonitic–granodioritic–porphyritic stock hosted by an Eocene volcanic sedimentary complex in which magmatic hydrothermal fluids were introduced and formed veins and alteration. Within the deepest quartz-rich and chalcopyrite-poor group A veins, LVHS2 inclusions trapped high salinity, high temperature aqueous fluids exsolved directly from a relatively shallow magma (0.5 kbar). These late fluids were enriched in NaCl and reached halite saturation as a result of the low pressure of magma crystallization and fluid exsolution. These fluids extracted Cu from the crystallizing melt and transported it to the hydrothermal system. As a result of ascent, the temperature and pressure of these fluids decreased from 600 to 415 °C, and approximately 500–315 bars. At these conditions, K-feldspar and biotite were stabilized. Type A veins were formed at a depth of ∼1.2 km under conditions of lithostatic pressure and abrupt cooling. Upon cooling and decompressing, the fluid intersected with the liquid–vapor field resulting in separation of immiscible liquid and vapor. This stage was recorded by formation of LVHS1, LVHS3 and VL inclusions. These immiscible fluids formed chalcopyrite–pyrite–quartz veins with sericitic alteration envelopes (B veins) under the lithostatic–hydrostatic pressure regime at temperatures between 415 and 355 °C at 1.3 km below the paleowater table. As the fluids ascended, copper contents decreased and these fluids were diluted by mixing with the low salinity-external fluid. Therefore, pyrite-dominated quartz veins were formed in purely hydrostatic conditions in which pressure decreased from 125 bars to 54 bars and temperature decreased from 355 to 298 °C. During the magmatic-hydrothermal evolution, the composition and P–T regime changed drastically and caused various types of veins and alterations. The abundance of chalcopyrite precipitation in group B veins suggests that boiling and cooling were important factors in copper mineralization in Darreh-Zar.     

河北唐山宋家营勘查区施工技术研究

宋家营勘查区位于河北唐山丰南区,存在着新生界厚度大,流沙层、卵石层、砂砾层松散破碎,部分钻孔漏失严重;煤层埋藏深、层数多、层位变化大等问题,给提高钻探施工质量和效益带来了不便。为解决这些问题,作者从钻孔设计人手,针对不同的地层采用相适应钻探工艺和技术措施,对长期沿用钻探方法进行改进,使钻进方法更具有针对性;对不同的地层配制了不同的冲洗液,对地层漏失根据情况采用恰当的堵漏方法,大大减少了因堵漏增加的成本。从而使钻进效率由过去的287m／台月,提高到440m／台月,台月效率提高了53．3％,大大降低了钻探成本。     

青海木里煤田永久冻土地层钻探技术研究

木里煤田属高寒缺氧地区,冻土（岩）层在钻进中遇热融解、融化,从而使孔内出现大范围的坍塌,造成卡钻、埋钻事故频发,给钻探施工及岩煤心采取带来很大的困难。从钻孔结构设计、钻具选择、低温冲洗液配置等方面进行深入研究,总结出来了一套适用于木里煤田永久冻土地层的钻探技术。应用表明,该项技术将钻月效率从2004年的224m,提高到2006年的424.5m,效果显著。