| Based on detailed evaluations of performance of the two employed portable X-ray fluorescence analysis (pXRF) instruments, combining in-situ grid analysis with image processing techniques and quantitative calculation methods like multivariate analysis, the paper rapidly identified minerals and clarified the mineralization paragenesis of hand specimens from the Jinding Pb-Zn deposit through characteristics of elemental distributions and elemental associations, and inferred the sources of ore-forming material of the Baiyinnuoer Pb-Zn deposit by comparing element migration characteristics of different dyke-wall rock interface outcrops, as well as quantitative evaluated the elemental migration and enrichment of the skarn outcrop.Most results obtained by the two instruments (EDX P730S and XL3t950) became relatively stable in or above40seconds of beam time, and a beam time of c.60seconds is adequate for analysis. In consideration of the degree of reading numbers close to the certified values of SRM2709a, the results of Fe, Mn, and Rb by P730S (short for EDX P730S) are better than that of P950(short for XL3t950), while the results of K, Ca, Ti, and Zr by P950are better than that of P730S. All results of Ca, Ti, Fe, and Sr by P730are great than certified values of SRM2709a, while K, Zn, and Zr less than certified values. All results of Ca, Ti, V, and Ni by P950are great than certified values, while K, Mn, Fe, Zn, Zr, Sr, and Rb less than certified values. Absolute content directly affects the accuracy and precision of instruments, that is, the bigger of the ratio of element content and LOD (short for manufacture’s limit of detector of instrument), the smaller of reading number error and variable coefficient, and vice versa. Sample surface covering material will result in reading number reducing synchronously, but does not affect the variable coefficient and stability of the results. As a result, results of batch samples obtained by pXRF in the same measurement condition can be used for trend analysis.Two typical hand specimens from the Jinding Pb-Zn deposit were measured by P730S. Mineral patterns were clearly visible in Specimen1, whereas eye identification of minerals in Specimen2was more difficult. Element content of hand specimen and morphology of minerals can be got visually through created element spatial distribution maps. Mineral species could be rapidly identified based on background-reference method and auxiliary-element method, combining with element content that can’t be obtained by naked-eye observation, which provided quantitative geochemical data as images for the study of mineralogy and mineralization. Three mineralization elemental associations of Pb+Bi+Cu+Ag+Sn+Ti, Zn+Co+Ni+Cd+Ti+Sb, and Fe+Mn were obtained by principal component analysis (PCA) from Specimen1, while Zn+Ni+Co+Sb+Cd+Ag+Mo+Fe+Cu, Pb+Bi, and Fe from Specimen2. Based on the principal of discriminating difference in formation time by element content and inferring sequence by favorable morphology, through relationships of replacement between minerals and characteristics of mineral morphology, mineralization sequences of the two specimens were inferred. Mineralization sequence of Specimen1was Fe+Mnâ†'Pb+Bi+Cu+Ag+Sn+Tiâ†'Zn+Co+Ni+Cd+Sb (+Ti), namely, on Fe-dominated mineralization superimposed Pb-dominated and Zn-dominated mineralization, while for Specimen2was Zn+Ni+Co+Sb+Cd+Ag+Mo+Fe+Cuâ†'Pb+Biâ†'Fe, namely Zn-dominated mineralization superimposed by later Pb-dominated mineralization, and Fe-dominated mineralization was later than the former two. These inferences were in agreement with observation results under the microscope. There was accompanying element Mn with similar property to that of Fe in relatively early Fe mineralization, whereas no Mn in later stage veined Fe mineralization, which can be used to discriminate Fe mineralizations of different periods. In both the two hand specimens, Zn mineralizations accompanied Co, Ni, Cd, and Sb (Ag, Mo, Cu), and Pb mineralizations accompanied Bi (Sn, Ag, Cu, Ti), namely, these elements had a close correlation with Pb and Zn mineralization, as a result, anomaly and paragenetic anomaly of these elements could be indicators for thermal Pb and Zn mineralization in the deposit.Different dyke-wall rock interface outcrops in the Baiyinnuoer Pb-Zn deposit were measured by P950, and following conclusions were drew through qualitative analysis on element spatial distributions:(1) There were no elemental migration and ore-forming element enrichment between quartz porphyry and marble;(2) Elements Ca and Si migrated in opposite directions and K was depleted in the felsic dyke-crystalline limestone interface outcrop. There were no migration of ore-forming elements like Zn, Pb in the outcrop except Fe and Mn showed a certain extent enrichment in the fading area near the interface.(3) In the granodiorite-marble interface outcrop, element Si migrated from granodiorite to marble, while ca the opposite direction. Potassium was strongly depleted in the altered granodiorite area. Ore-forming elements Zn, Pb, Fe, Mn, Cu, As, etc. were enriched remarkablely in the skarn between granodiorite and marble, moreover, showed a spatial zoning of Cu, As and Zn, Pb, Fe.Characteristics of elemental migration demonstrated that the formation of skarn and the enrichment of ore-forming elements in the granodiorite-skarn-marble interface outcrop (skarn outcrop) had a close correlation with wall rocks especially the granodiorite, as well as skarn mineral veins were found to insert into altered granodiorite and sulfide minerals were formed mainly in the skarn-marble interface, these phenomena supported the conclusion that skarns in research area were formed due to contact metasomatism but not deposition, further, the Baiyinnuoer Pb-Zn deposit was a skarn deposit. Based on in-situ geochemical element migration study, following conclusions were drew:the quartz porphyry contributed nothing to ore-forming; though there were a certain extent element migration, no ore-forming elements were enriched in the interface between felsic dyke and crystalline limestone; ore-forming elements strongly enriched in the skarn area between granodiorite and marble, and granodiorite provided some or all of the ore-forming materials in the research area. The first four principal components obtained by PCA of the skarn outcrop represent the marble, diorite, and two stages of mineralization of skarn type. The two stages of mineralization in the hedenbergite skarn may occur as earlier mineralization dominated by chalcopyrite-sphalerite and later mineralization by sphalerite-galena-pyrite. Elements Ca, Mg, K, Rb, and Ba can be found in both the two mineralization principal components, which imply that these five elements were active in the process of skamization and had a close correlation with mineralization. The Ca and Mg that originated from marble and the K, Rb, and Ba that originated from diorite simultaneously appear in the mineralized skarn, indicating a genetic relation between mineralization and skam formation and the inheritance relationship between the mineralization and the skamization of marble and diorite.Quantitative calculation of element migration and enrichment index were conducted on the pXRF data of the skarn outcrop. The altered granodiorite near the skran depleted K, Ba, Rb, and Cl compared to its protolith, and Ca, Mg, Si, Al, S, Fe, Mn, Pb, Zn, and Cu were enriched, while the marble near the skarn depleted K, Ba, and Cl compared to its protolith, and Rb, Si, Al, S, Fe, Mn, Pb, and Cu were enriched. Compared to granodiorite, the skarn depleted K, Ba, Rb, and Cl, and Ca, Mg, Si, Al, Zn, Pb, Fe, Mn, Cu, and S were enriched, while compared to the marble, the skam K, Ba, Cl, Ca, and Mg, and Rb, Si, Al, Zn, Pb, Fe, Mn, Cu, and S were enriched. It can be inferred that relative active elements K, Ba, and Cl were carried away by hydrothermal liquid during the process of skamization, and Si, Al, Zn, Pb, Fe, Mn, Cu, and S were brought and enriched. Elements Si and Al migrated from the granodiorite to the marble, while Ca and Mg from the marble to granodiorite. The order of elements with element enrichment from high-to low-degree in the skam compared to the granodiorite were S, As, Pb, Mn, Ca, Zn, Mg, Fe, Al, Si, and Sr, while for element depletion were K, Cl, and Sr. The order of elements with element enrichment from high-to low-degree in the skam compared to the marble were Pb, As, Mn, Cu, Mg, Fe, Si, S, Zn, Sr, and Al, while for element depletion were Cl, Ca, K, Zn, Sr, and Al. It can be inferred that ore-forming elements mainly came from hydrothermal liquid originated from granodiorite. Moreover, element Zn showed both enrichment and depletion in the skarn compared to the marble, which implied that the marble may provide part of element Zn. |
PDF Full Text Request