Mineral zoning and gold occurrence in the Fortuna skarn mine, Nambija district, Ecuador   总被引：1，自引：0，他引：1  

Agnès Markowski  Jean Vallance  Massimo Chiaradia  Lluìs Fontboté 《Mineralium Deposita》2006,41(4):301-321

The Fortuna oxidized gold skarn deposit is located in the northern part of the Nambija gold district, southern Ecuador. It has been subdivided into four mineralized sites, covering a distance of 1 km, which are named from north to south: Cuerpo 3, Mine 1, Mine 2, and Southern Sector. Massive skarn bodies occur in K–Na metasomatized volcanic and volcaniclastic rocks of the Triassic Piuntza unit. They appear to result from selective replacement of volcaniclastic rocks. Very minor presence of bioclast relicts suggests the presence of subordinate limestone. Endoskarn type alteration with development of Na-rich plagioclase, K-feldspar, epidote, actinolite, anhedral pyroxene, and titanite affects a quartz–diorite porphyritic intrusion which crops out below the skarn bodies in Mine 2 and the Southern Sector. Endoskarn alteration in the intrusion grades into a K-feldspar ± biotite ± magnetite assemblage (K-alteration), suggesting that skarn formation is directly related to the quartz–diorite porphyritic intrusion, the latter being probably emplaced between 141 and 146 Ma. The massive skarn bodies were subdivided into a dominant brown garnet skarn, a distal green pyroxene–epidote skarn, and two quartz-rich varieties, a blue-green garnet skarn and light green pyroxene–garnet skarn, which occur as patches and small bodies within the former skarn types. The proximal massive brown garnet skarn zone is centered on two 060° trending faults in Mine 2, where the highest gold grades (5–10 g/t) were observed. It grades into a distal green pyroxene–epidote skarn zone to the North (Cuerpo 3). Granditic garnet shows iron enrichment from the proximal to the distal zone. Diopsidic pyroxene exhibits iron and manganese enrichment from proximal to distal zones. The retrograde stage is weakly developed and consists mainly of mineral phases filling centimeter-wide veins, vugs, and interstices between garnet and pyroxene grains. The main filling mineral is quartz, followed by K-feldspar, epidote, calcite, and chlorite, with minor sericite, apatite, titanite, hematite, pyrite, chalcopyrite, and gold. Metal and sulfur contents are low at Fortuna, and the highest gold grades coincide with high hematite abundance, which suggests that retrograde stage and gold deposition took place under oxidizing conditions. Fluid inclusions from pyroxene indicate precipitation from high temperature—high to moderate salinity fluids (400 to 460°C and 54- to 13-wt% eq. NaCl), which result probably from boiling of a moderately saline (∼8-wt% eq. NaCl) magmatic fluid. Later cooler (180 to 475°C) and moderate to low saline fluids (1- to 20-wt% eq. NaCl) were trapped in garnet, epidote, and quartz, and are interpreted to be responsible for gold deposition. Chlorite analysis indicates temperature of formation between 300 and 340°C in accordance with fluid inclusion data. It appears, thus, that gold was transported as chloride complexes under oxidizing conditions and was deposited at temperatures around 300°C when transport of chloride complexes as gold carriers is not efficient.  相似文献   

Shopping to save lives: Gender and environment theories meet ethical consumption     

Roberta Hawkins 《Geoforum》2012,43(4):750-759

Much of the current work in the field of ‘gender and environment’ has been developed around case studies of environmental roles, rights and responsibilities at the community or household scale in the South. This paper asserts that the theoretical insights developed through these case studies can be of great use when examining issues of gender and environment in the North, particularly when it comes to issues of ethical consumption. In this paper I examine the promotional discourses of two cause-related marketing (CRM) campaigns (where consumption of a CRM product triggers a donation to a development cause) using two such insights: (i) the mutual constitution of gendered subjectivities and environments and (ii) a gender and environment approach to questioning neoliberalization. This approach highlights the ways in which – through consumption – gender is constituted transnationally at the same time that it is constituted in relation to environments. This approach also emphasizes a series of questions about the neoliberal aspects of CRM campaigns that are usually hidden behind discourses of motherhood and responsibility. Overall, I argue that bringing gender and environment and ethical consumption research together allows us to advance both areas of study in critical and insightful ways.  相似文献   

Landslide susceptibility assessment in Apulian Southern Apennine: heuristic vs. statistical methods   总被引：2，自引：1，他引：1  

Roberta Pellicani  Paolo Frattini  Giuseppe Spilotro 《Environmental Earth Sciences》2014,72(4):1097-1108

In this paper, a bivariate-heuristic model (modified Stevenson’s method) and two multivariate statistical procedures (discriminant analysis and logistic regression) were used in order to assess and map landslide susceptibility in the north-western side of Daunia region (Apulia, Southern Italy). The whole Daunia region is characterized by complex and composite landslides, which are located on clayey slopes, near urban centers, affecting structures and infrastructures. The high predisposition to landsliding of the Daunia hillslopes is related to the very poor strength properties of clayey formations. The comparative analysis of landslide susceptibility using different methods, on the same test site and with the same inventory map allowed understanding the dependence of the results from the dataset and the capability of models under different levels of use, from expert to simple operator. By comparing the performance of the three models through the success rate curves, it emerges that the simple modified Stevenson’s method produces reliable outcomes, comparable with those deriving from more complex multivariate statistical models. This result is related to the characteristics of clayey slopes, in which the landslide occurrence is so much controlled by the poor strength properties of the clayey formations that the multivariate analysis of a large set of morphometric, geological and land-use variables results to be somehow superfluous. This suggests that, for clayey slopes, a simple, easy-to-manage bivariate-heuristic model based on expert opinion can be used with reliable results.  相似文献