Mineralogy and Mode of Occurrence of Gold, Silver and Bismuth of the Caijiaying Lead-Zine-Silver Deposit, Hebei Province

The deposit under study is a hydrothermal filling-metasomatic vein type lead-zinc-silver deposit, in whichgold and silver can be recovered as by-products. These metals mainly occur as microgranular native gold,electrum, stephanite, acanthite, pyraragyrite, freibergite, and native silver. Gold minerals tend to be associatedwith galenobismutite, native bismuth and unnamed Bi_2Te. They are either enclosed in pyrite, marmatite,iron-bearing sphalerite and galens or fill the microfissures of these minerals. Silver minerals usually occur incleavages or fissures of galena, marmatite and pyrite, but are not associated with gold and bismuth minerals.Gold and silver mineralizations occurred later than lead and zinc, while the silver mineralization was precededby that of gold.     

Experimental Study on Gold Dissolution from Hosting Minerals of the Hadamengou Gold Deposit and the Implications

The Hadamengou gold deposit is located in western part of the northern margin of the North China craton. It is a hydrothermal deposit related to alkaline magmatism. Dissolution of Au, Fe from pyrite and iron oxide （including magnetite and hematite） individual minerals in the three main types of ore shows： in iron oxides （magnetite and hematite）, Au and Fe were dissolved simultaneously and their solubilities are positively correlated, which means Au is mainly chemical-bonded （lattice gold） and/or colloidal-adsorbed in iron oxides; while in pyrite, on the contrary, Au dissolution obviously lags behind Fe and the solubility of Au shows negative relationship with that of Fe, which indicates Au is mainly hosted as grains of elemental gold （or native gold） within pyrite. Previous studies revealed that the Hadamengou gold deposit is characterized by intensive K-feldspathization and holds high content of iron oxides occasionally replaced by sulfides, which was caused by oxidizing K-enriched alkaline fluids under a stretching geodynamic setting. These geological features, together with the high Au-content in iron oxides, comparable with that of the Olympic Dam deposit in South Australia, suggest that this deposit is the first example of iron oxide-type gold deposits in China.     

Zinccopperite-A New Variety of Zinc-CopperIntermetallic Compounds Discovered in aPorphyry-Copper Deposit

Zinccopperite (tentatively named) is a rare native alloy mineral discovered in quartz monzonite-porphyry in the Xifanping area, Yanyuan County, Sichuan Province. It is a new variety of zinc-copper alloy mineral found for the first time in the porphyry-copper deposit in China. Its intergrown minerals are K-feldspar (mainly perthite), albite-oligoclase, quartz and biotite; and the associated minerals include pyrite and chalcopyrite. It is characterized by a golden reflection colour, being isotropic (isometric), with the grain size ranging from 10 to 50 μm, microhardness VHN10= 190 kg/mm2, and reflectance RVis= 67.97%. Electron microprobe (Model JXA-733) analysis shows Cu = 59.15%-62.55% and Zn= 36.32%-39.85%. The crystallochemical formula is Cu6.27-7.0Zn4.0, simplified as Cu7Zn4.     

Typomorpic Characteristics of the Major Minerals in the Puziwan Gold Deposit, Datong, Shanxi, China

Utilizing theories of minerageny and prospecting mineralogy, the authors studied the attitude, morphotype and chemical composition of metallic minerals of pyrite, gold, chalcopyrite, galena and sphalerite, non-metallic minerals of quartz, carbonate, dolomite and rutile in the Puziwan gold deposit. The study shows the following results. （1） The mineral assemblage is complex and the species of sulfide are abundant with occurrences of sulfosalt minerals. （2） The composition in the minerals is complex and there rich micro elements, including As, Sb, Bi, Se, Te, Au, Ag, Cu, Pb, Zn, and Cr, Ni, V. The typomorphic characteristics of the association of the elements and their specific value suggest that gold mineralization is associated with shallow magmatic hydrothermal activity, the oreforming fluid is the mixture of abundant rising alkali magmatic water originating from the mantle or the lower crust and the descending acid atmospheric water. （3） Ankerite, Fe-rich sphalerite, granular Ti-rich rutile are widely distributed, which indicate great denudation depths, high mineralization temperature. The deposit is found in the middle and shallow positions of the porphyry series. The deep layers are not favorable for gold mineralization. （4） Copper minerals are rich in the ores and sulfides have high content of copper, suggesting possible porphyry-type Cu （Au） mineralization in deep positions and the surrounding areas.     

Discovery,Genesis and Significance of Metallic Minerals in Evaporate Series in the Kuqa Basin

A large-scale evaporate series is developed in Paleogene-Neogene strata in the Kuqa basin. The series is composed mainly of evaporate with thin beds of clastic rock (mainly mudstone and siltstone). In grayish white medium- and coarse-grained sandstone in Miocene strata, the formation of copper minerals is in close connection with brine. In joint planes, which are developed in vertical strata, are filled with gypsum. Gypsum and copper-mineralized sandstone contains enormous copper minerals, mainly atacamite. According to the SEM analysis for salt rock, gypsum rock, limestone, grayish green siltstone, grayish white medium-coarse-grained sandstone, some minerals are composed of metallic elements including Au, Ag, Cu, Zn, Pb, Co, Ni and U etc., in which Au occurs in a native form, Cu occurs in a native form or as atacamite in salt rock, gypsum rock and limestone, Ag occurs as silver sulfide in gypsum, and Zn, Pb, Co, Ni, U occur as compounds along with the above metallic ions in evaporate or clastic rock. From SEM images, we can see that metallic elements or their compounds (oxides or sulfides) “take root” as grains in salt or gypsum crystals, which belong to primary chemical sedimentation along with evaporate, while some grains “float” on surface of salt or gypsum. In the former case, mineral grains were formed together with salt (gypsum) crystals; while in the latter case, minerals were enriched from internal metallic ions (Paleogene evaporate samples) or external metallic ions (Neogene gypsum samples) in the late stage of evaporate formation. The metallic ions in Paleogene evaporate samples might originate from weathered or denudated materials in the south Tianshan Mountains. The metallic ions in the Neogene evaporate samples might be from metal-bearing brine, which migrated upward to surface along fractures and leached into evaporate (gypsum). Occurrence of metallic minerals and their compounds (elementary substance) in Paleogene evaporate proves that diversified metallic minerals exist in evaporate. The source of metallic ions in the Neogene evaporate series shows that evaporate could provide materials for late-stage metallic mineralization.     

Study on the Physical and Chemical Conditions of Ore Formation of Hetai Ductile Shear Zone—Hosted Gold Deposit and Discovery of Melt Inclusions

The Hetai ductile shear zone-hosted gold deposit occurs in the deep-seated fault mylonite zone of the Sinian-Silurian metamorphic rock series. In this study there have been discovered melt inclusions, fluid-melt inclusions and organic inclusions in ore-bearing quartz veins of the ore deposit and mylonite for the first time. The homogenization temperatures of the various types of inclusions are 160℃, 180 - 350℃, 530℃ and 870℃ for organic inclusions, liquid inclusions, two-phase immiscible liquid inclusions and melt inclusions, respectively. Ore fluid is categorized as the neutral to basic K+ -Ca2+ -Mg2+ -Na+ - SO2- 4-HCO3-Cl- system. The contents of trace gases follow a descending order of H2O＞CO2＞CH4＞(or ＜ ) H2＞CO＞C2H2＞C2I-I6＞O2＞N2.The concentrations of K , Ca2 + ,SO2-4,HCO3-,Cl- H2O and C2H2 in fluid inclusions are related to the contents of gold and the Au/Ag ratios in ores from different levels of the gold deposit. This is significant for deep ore prospecting in the region. Daughter minerals in melt inclusions were analyzed using SEM. Quartz, orthoclase, wollastonite and other silicate minerals were identified. They were formed in different mineral assemblages.This analysis further proves the existence of melt inclusions in ore veins. Sedimentary metamorphic rocks could form silicate melts during metamorphic anatexis and dynamic metamorphism, which possess melt-solution characteristics. Ore formation is related to the multi-stage forming process of silicate melt and fluid.     

A New Mechanism of Formation of the Silver—Rim Structure on Primary Gold Grains

Gold minerals in the Baochun skarn-type gold deposit are Au-Ag allogy with Ag contents within the range of 15-35.5wt% and the inerals vary from 5μm to 50μm in size.As viewed from the electron microprobe images,most gold grains show silver rims with a high Ag content as compared with the core,ranging generally from 2 to 3μm in width.From dynamic calculations based on the mass action and mass balance constratints on the crystallization of native gold,it is considered that the enrichment of silver in the rim of gold minerals in due to gradual enrichment of silver in the ore-forming solutions with its evolution from the early to the late metallogenic stage.     

Newly Discovered Native Gold and Bismuth in the Cihai Iron-Cobalt Deposit, Eastern Tianshan, Northwest China

The Cihai iron-cobalt deposit is located in the southern part of the eastern Tianshan ironpolymetallic metallogenic belt. Anomalous native gold and bismuth have been newly identified in Cinan mining section of the Cihai deposit. Ore formation in the deposit can be divided into three stages based on geological and petrographical observations:(I) skarn, with the main mineral assemblage being garnet-pyroxene-magnetite;(II) retrograde alteration, forming the main iron ores and including massive magnetite, native gold, native bismuth, and cobalt-bearing minerals, with the main mineral assemblage being ilvaite-magnetite-native gold-native bismuth; and(III) quartz-calcitesulfide assemblage that contains quartz, calcite, pyrrhotite, cobaltite, and safflorite. Native gold mainly coexists with native bismuth, and they are paragenetically related. The temperature of initial skarn formation was higher than 340℃, and then subsequently decreased to ~312℃ and ~266℃. The temperature of the hydrothermal fluid during the iron ore depositional event was higher than the melting point of native bismuth(271℃), and native bismuth melt scavenged gold in the hydrothermal fluid, forming a Bi-Au melt. As the temperature decreased, the Bi-Au melt was decomposed into native gold and native bismuth. The native gold and native bismuth identified during this study can provide a scientific basis for prospecting and exploration for both gold- and bismuth-bearing deposits in the Cihai mining area. The gold mineralization in Cihai is a part of the Early Permian Cu-Ni-Au-Fe polymetallic ore-forming event, and its discovery has implications for the resource potential of other iron skarn deposits in the eastern Tianshan.     

The Existence of the Negative Charge of Gold in Sulphide Minerals and Its Formation Mechanism

Through a study, particularly an X-ray photoelectron spectroscopy (XPS or ESCA) analysis, of gold-bearing arsenopyrite and pyrite in Carlin-type gold deposits of Guangxi, China, and hydrothermally synthesized gold-bearing pyrite and marcasite, the authors have found that these minerals contain "invisible gold" whose binding energy is lower than that of native gold (Au°). Therefore they suggest that gold occurs in a negative charge state in these sulphide minerals as it replaces some sulphur and is combined with sulphur with the covalent bond. This paper also preliminarily discusses the possibility of its formation from the chemistry and geochemistry of gold, crystal chemistry of arsenopyrite, pyrite and marcasite and geochemical environment.     

Luobusaite： A New Mineral

A group of mantle minerals including about 70-80 subtypes of minerals are discovered from a podiform chromitite in Tibet, China. Recovered minerals include diamond, coesite, moissanite, wustite, Fe-silides and a new mineral, luobusaite. All of these minerals were hand-picked from heavymineral separates of the podiform chromitite in the mantle peridotite of an ophiolite. The grains of luobusaite are as host mineral with inclusions of native silicon or as an intergrowth with native silicon and Fe-Si phase. Luobusaite occurs as irregular grains, with 0.1-0.2 mm in size, consisting of very finegrained aggregates. The mineral is steel-grey in color, metallic luster, and opaque. The empirical formula （based on 2 for Si） is Fe0.83Si2, according to the chemical compositions of luobusaite. X-ray powder-diffraction data： orthorhombic system, space group Cmca, a = 9.874 （14） A, b = 7.784 （5） A, c= 7.829（7） A, Z=16.     

Geochemical Styudy of Gold and Arsenic Mineralization of the Carlin-Type Gold Deposits,Qinling Region,China

Element geochemistry of gold arsenic and mineralogical features of their sulfides in the Carlin-type gold depostis of the Qinling region are discussed in this paper.The initial contents of ore-forming elements such as glod and arsenic are high the ore-bearing rock series in the Qinling region.Furthermore,both the metals are concentrated mainly in the diagenetic pyrite.Study on the mineralogy of arsenic-bearing sulfide minerals in the ores demonstrated that there is a poistive correlation between gold and arsenic in the sulfide minerals.Available evidence suggests that gold in the As-bearing sulfide minerals in likely to be presented as a charge species(Au ),and it is most possible for it to replace the exxcess arsenic at the site of iron and war probably deposited together with arsenic as solid in the sulfide minerals. Pyrite is composed of(Aux^3 ,Fe1-2^2 )([AsS]x^3-[S2]1-x^2-),and arenopyrite of (Aux^3 ,Fe1-x^3 )([AsS]x^3-[AsS2]1-x^3-).The occurrence of glod in the As-sulfied minerals from the Carlin-type gold depostis in the Qinling region has been confirmed by electron probe and transmission electron microscopic studies.The results show that gold was probably depostied together with arsenicas coupled solid solutions in sulfide minerals in the early stage of mineralization.Metallogenic chemical reactions concerning gold deposition in the Carlin-type As-rich gold deposits would involve oxidation of glod and concurrent reduction of arsenic.Later,the deposited gold as solid was remobilized and redistributed as exsolutions,as a result of increasing hydrothermal alteration and crystallization,and decreasing resistance to refractoriness of the host minerals.Gold occurs as sub-microscopic grains(ranging from 0.04tp 0.16μm in diameter)of native gold along micro factures in and crystalline grains of the sulfiedes.     

Laumontitization as an Exploration Indicator of Epithermal Gold Deposits： A Case Study of the Axi and Other Epithermal Systems in West Tianshan, China

In the light of field investigation, microscopic study, X-ray phase analysis and mineral infrared spectral analysis, it is considered that laumontitization is of extensive occurrence in the Axi gold orefield. The development of laumontitization and its relationship to mineralization show that the laumontitization appeared mainly at the top of and in the periphery of orebodies, and occurred at the edge of the epithermal system or at the late stage of epithermal system evolution. Therefore, laumontitization can be used as an exploration indicator of epithermal gold deposits. The fluids responsible for laumontitization in the Axi gold orefield are similar to those producing hot spring-type gold deposits or those from modem geothermal fields. Epithermal mineralization of the Axi gold deposit was dated at Carboniferous, indicating that the West Tianshan of China is a region favorable to epithermal-type gold mineralization and preservation. Hence the West Tianshan of China is a target area for exploring epithermal gold deposits.     

Chemical composition of the ore and occurrence state of the elements in Jingbaoshan platinum-palladium deposit

The Jingbaoshan platinum-palladium deposit is China＇s largest independent PGM （platinum-group metals） deposit so far discovered. There are eleven kinds of useful components in the ore： Pt, Pd, Os, Ir, Ru, Rh, Au, Ag, Cu, Ni, and Co. The platinum-group elements, gold and silver occur in the form of minerals in ores. twenty-five kinds of precious metal minerals have been found, of which twenty one belong to the platinum-group minerals. The minerals are very small in grain size. Copper occurs mainly as copper sulfide with a small amount of free copper oxide, and the beneficiated copper accounts for 95.21%. Nickel occurs mainly as nickel sulfide, and some nickel silicate and nickel oxide occur in the ore. The beneficiated nickel accounts for 72.03%. Cobalt occurs mainly as cobalt sulfide, and there are some cobalt oxide and other kinds of cobalt. The beneficiated cobalt accounts for 77.58%.     

The geochemical multi-fractal characteristics and mineralization of the Dehelongwa copper-gold deposit

The spatial distribution of ore-forming elements is the result of interaction and influence among multiple factors in the process of mineralization, and is the specific embodiment of non-linearity and coupling of mineralization. The fractal theory has such functions as to characterize non-lineariry and coupling, and can find out the deterministic law from the complicated coupling process. The primary geochemical fractal distribution of metallogenic elements such as Cu and Au possesses the characteristics of multi-fractal distribution in the Dehelongwa copper-gold deposit. Copper follows 2-d fractal distribution, and Au follows 3- or 4-d fractal distribution. The primary geo- chemical fractal distribution has a certain similarity on the same prospecting line, and this similarity is not obvious among different prospecting lines. The secondary geochemical fractal distribution of Cu and Au is higher in similar- ity, and simpler than the primary geochemical fractal distribution. These results show that the mineralization of Cu and Au is out of sync and also is inconsistent in this deposit, and the mineralization of Cu mainly experienced two mineralization stages, while the mineralization of Au experienced three to four mineralization stages. Besides the mineralization of Cu and Au shows a certain direction and along the strike of vertical orebodies it is relatively bal- anced. While along the strike of the ore bodies the mineralization of Cu and Au shows a significant difference. The hypergenic geologic process has a certain effect on the balance of spatial distribution of Cu and Au. From these it can be seen that the mineralization process of this deposit is well characterized by the geochemical fractal distribu- tion of Cu and Au.     

Characteristics and Genesis of the Aktubaik Gold Deposit in Altay, Xinjiang

The Aktubaik gold deposit lies in the Altay middle-high mountains area, Xinjiang, hosted by the Pa-laeo- and Mesoproterozoic Xemirxek Group. It is the first gold deposit found in Precambrian rocks in Altay. The deposit is controlled by the NW-trending fracture-alteration zone, in which rocks have been strongly altered and bleached. The main wall-rock alterations include silicification, sericitization (muscovitization), carbonation, pyritiza-tion and tourmalinization. Several gold mineralization zones of this type have been found in the study area. The dominant gold mineral is native gold, which is distributed very unevenly, so special methods such as peeling and bulk sampling are required in exploration. The discovery of this gold deposit has laid a foundation for gold exploration in Precambrian rocks in the Altay middle-high mountains area, Xinjiang.     

Study on Mineralization Age of Xiaoban Gold Deposit, Fujian Province

The Xiaoban gold deposit is a large-size deposit recently found in middle area of Fujian Province. It belongs to magmatic hydrothermal type occurred in Mayuan Group metamorphic rocks of Middle Proterozoic and is controlled by low angle fault (detachment) structures. The contents of Au in Mayuan Group metamorphic rocks, Caledonian-Indosinian deformed granite and early Yanshanian granite are higher with Au enrichment coefficient of 2.06-5.68, 5.11 and 6.67 than those in other geological bodies. And the higher enrichment coefficients (>2) of Ag, S, Sn and Te are similar to those of gold ore. Meanwhile, the distribution of Au in Mayuan Group metamorphic rocks and early Yanshanian granite with a low D-value (0.58 and 0.67) is favorable to gold mineralization. REE characteristics of gold ore, ratios of (LREE/HREE), (La/Sm)n, (Yb/Lu)n, (La/Tb)n and (Sm/Nd)n are similar to Mayuan Group metamorphic rocks, only non or little normal Eu abnormal of ore is dissimilar to metamorphic rocks. The δ(34S) of the gold ore, with a high homogenization, is (-4.7×10-3)-(-2.7×10-3). The study of inclusion indicates 180-249 ℃ of mineralization temperature, 3.69 %-11.81 % of salinities and 0.869-0.991 g/cm3 of densities of mineralization fluid. Based on hydrogen and oxygen isotope (δ(18O)=11.0×10-3-11.7×10-3, δ(D)=(-48×10-3)-(-62×10-3)) and initial w(87Sr)/w(86Sr) =0.715,combining to the analysis of geological history, regional metamorphism and magamtic activity, the authors confirm that the source for the ore fluid was mainly from magmatic, partly from metamorphic water, and with a little influence of meteoric water. Isotopic dating made on Rb-Sr isochron age of 182 Ma, by using alteration minerals of gold-ores from the deposit, indicates that the mineralization occurs in early Yanshanian epoch. This is close to the age of 187 Ma of the Anchun magmatite with a similar alteration and gold mineralization to the Xiaoban gold deposit. The age of early Yanshanian epoch of the Xiaoban gold is indentical with the characteristics of southern China gold metallogenic belt and the geotectonic evolution of the transition from paleo-Asian system and paleo-Tethyan system to paleo-Pacific active continental margin in eastern Asia.     

On the metallogenesis of Dajing Cu-Sn-polymetallic ore deposit, Inner Mongolia, China

The Dajing Cu-Sn-polymetallic ore deposit is famous for its large scale, abundant associated elements, narrow and closely-spaced development of ore veins and high grade, but exploration within the mining district and its deeper parts has revealed no Yanshanian rockbody. Therefore, there have been proposed a diversity of hypotheses on the genesis of the deposit. The authors, from the angle of mantle-branch structure, provided evidence showing that the mining district is located in the core of the Da Hinggan Ling mantle-branch structure, the multi-stage evolution of mantle plume paved the way for the ascending of deep-source ore fluids and these fluids extracted part of the ore-forming materials. Then, these ore-forming materials were concentrated in the favorable structural loci (e.g. structural fissures) to form ores. The orientation of ore-forming and ore-controlling fissures is closely related to the regionally structural stress field at the metallogenic stage. The zonation of Sn, Cu, Au, Ag, Pb, and Zn within the mining district appears to be related to metallogenesis and the crystallization temperature of ore-forming materials. Mineralization of Sn, Cu, Au, etc. which require relatively high crystallization temperature and pressure is in most cases recognized in the central part of the mining district, while that of Ag, Pb, Zn, etc. which require relatively low crystallization temperature and pressure is, for the most part, produced in the periphery of the mining district.     

Distribution Characteristics of Gold and Other Trace Elements in the Proterozoic Lengjiaxi Group,Northeastern Hunan Province

Systematic geochemical studies of the Proterozoic Lengjiaxi Group in northeastern Hunan Province suggest that the Lengjiaxi Group is a Au-As-Sb-W association-type Au-bearing turbidite formation.The contents of Au,As,Sb,W,Cr,Mn,Pb and Zn in the turbidite formation are more than two times as high as the average contents of trace elements in the upper continental crust.The low abundance of Ag and the close correlation between Au and As are two important characteristic features.In the Au-bearing turbidite formation the enrichment of gold is due to the extensive occurrence of Au-bearing pyrites.Higher contents of Au,W,Sb and Ag in the greywacke indicate that they also exist in the form of heavy minerals.Au,Ag,As,Sb,W and REE in the Au-bearing turbidite formation have a close genetic relation with the chemistry of the gold deposits.     

The Discovery of Magnesioferrite from Au (Fe, Cu) Magnesian Skarn Deposits and Study of the Magnesioferrite-Magnesiomagnetite Series

Magnesioferrite, a rare metasomatic mineral, was discovered for the first time in China from the Qinlou Au (Fe, Cu) magnesian skarn deposit, Sanpu, Huaibei, Auhui Province, and the Mulonggou Fe (Mo, Cu) magnesian skarn deposit, Luonan County, Shaanxi Province. In this paper, the geological setting, mineral associations, chemical composition, some physical properties, X-ray powder diffraction data and infrared spectroscopy of magnesioferrite and magnesiomagnetite are discussed. Magnesioferrite contains 17.66%-13.48% of MgO. Its main associated minerals are clinohumite, chondrodite, serpentine,, calcite and magnesiomagnetite. The density of magnesioferrite is 4.537-4.720, reflectances in percent are: 17.8-18.1, hardness is 838-900 kg/mm2, and the cell parameter a0 = 8.371-8.379 A. A systematic study of the magnesioferrite-magnesiomagnetite-magnetite series suggests that along with the increase of magnesioferrite molecules in the mineral, the density, reflectances and cell parameters decrease corresponding     

Geochemical Characteristics and Zonation of Primary Halos of Pulang Porphyry Copper Deposit,Northwestern Yunnan Province,Southwestern China

The Pulang (普朗) porphyry copper deposit, located in the southern segment of the Yidun-Zhongdian (义敦-为中甸) island arc ore-forming belt of the Tethys-Himalaya ore-forming domain, is a recently discovered large copper deposit. Compared with the composition of granodiorite in China, the porphyry rocks in this area are enriched in W, Mo, Cu, Au, As, Sb, F, V, and Na2O (K1≥1.2). Compared with the composition of fresh porphyry rocks in this district, the mineralized rocks are enriched in Cn, Au, Ag, Mo, Pb, Zn, W, As, Sb, and K2O (K≥1.2). Some elements show clear anomalies, such as Zn, Ag, Cu, Au, W, and Mo, and can be regarded as pathfinders for prospecting new ore bodies in depth. It has been inferred from factor analysis that the Pulang porphyry copper deposit may have undergone the multiple stages of alteration and mineralization: (a) Cu-Au mineralization; (b) W-Mo mineralization; and (c) silicification and potassic metasomatism in the whole ore-forming process. A detailed zonation sequence of indicator elements is obtained using the variability index of indicator elements as follows: Zn→Ag→Cu→Au→W→Mo. According to this zonation, an index such as (Ag×Zn) D/(Mo×W) D can be constructed and regarded as a significant criterion for predicting the Cu potential at a particular depth.