ABSTRACT
Locating mineral deposits in areas of thick or transported overburden is notoriously difficult. Post-mineral cover is prevalent in many parts of the globe and has led to prospective geological sequences being missed by traditional methods of exploration. Hydrogeochemistry is particularly applicable for the exploration of Iron Oxide Copper Gold (IOCG) deposits because, when compared to larger porphyry or sediment-hosted systems, IOCG deposits tend to be smaller and high-grade with a limited lateral footprint to intersect with grid-drilling; groundwater interactions and ion dispersion tend to produce a much larger anomaly target than regolith geochemistry alone and require fewer samples. As a case study, we examine the hydrogeochemistry of the Kitumba IOCG deposit, located in the Mumbwa district of west-central Zambia. We present physicochemical data (Eh, pH, TDS, conductivity), major and trace element concentrations, and isotopic compositions (δ98Mo, 87Sr/86Sr, and δ65Cu) from groundwaters interacting with the Kitumba deposit and surrounding prospects. A hydrogeochemical footprint of As, Mo, Fe, Mn, and Zn is dispersed from the deposit. Groundwater 87Sr/86Sr values (0.708832 to 0.731807) reflect the mixing in varying proportions of waters that have interacted with distinct lithological endmembers in the Mumbwa area, corresponding to a complicated tectonic and metamorphic history. We report fractionation of 1.34 to 1.60 (∆65Cugroundwater - chalcopyrite) between proximal groundwater and primary chalcopyrite, which we postulate may be related to the oxidative dissolution of primary sulfide minerals. The δ98Mo3134 values of groundwaters proximal to known ore bodies are isotopically distinct (-1.08 ± 0.18 2SE to 0.64 ± 0.08 2 SE) from background aquifers (2.08 ± 0.12 2SE). The trace element and isotopic hydrogeochemical patterns described in this study document water-rock and water-deposit interactions and demonstrate the potential of non-traditional stable isotopes to be employed in district-scale reduction of exploration ground and vectoring towards undisturbed ore deposits similar to Kitumba.
Subject(s)
Groundwater , Water Pollutants, Chemical , Minerals , Prospective Studies , Water Pollutants, Chemical/analysis , ZambiaABSTRACT
BACKGROUND: The chromophobe subtype represents the third most common histological subtype of renal cell carcinoma (chRCC). Due to the rarity of this subtype only one publication regarding the specific analysis of clinical and histopathological criteria as well as survival analysis of more than 200 patients with chRCC is known to date. MATERIALS AND METHODS: A total of 6,234 RCC patients from 11 centres who were treated by (partial) nephrectomy are contained in the database of this multinational study. Of the patients 259 were diagnosed with chRCC (4.2 %) and thus formed the study group for this retrospective investigation. These subjects were compared to 4,994 patients with a clear cell subtype (80.1 %) with respect to clinical and histopathological criteria. The independent influence of the chromophobe subtype regarding tumor-specific survival and overall survival was determined using analysis by Cox proportional hazards regression models. The median follow-up was 59 months (interquartile range 29-106 months). RESULTS: The chRCC patients were significantly younger (60 vs. 63.2 years, p < 0.001), more often female (50 vs. 41 %, p = 0.005) and showed simultaneous distant metastases to a lesser extent (3.5 vs. 7.1 %, p = 0.023) compared to patients with a clear cell subtype. Despite a comparable median tumor size a ≥ pT3 tumor stage was diagnosed in only 24.7 % of the patients compared to of 30.5 % in patients with a clear cell subtype (p = 0.047). In addition to the clinical criteria of age, sex and distant metastases, the histological variables pTN stage, grade and tumor size showed a significant influence on tumor-specific and overall survival. However, in the multivariable Cox regression analysis no independent effect on tumor-specific mortality (HR 0.88, p = 0.515) and overall mortality (HR 1.00, p = 0.998) due to the histological subtype was found (c-index 0.86 and 0.77, respectively). CONCLUSIONS: Patients with chRCC and clear cell RCC differ significantly concerning the distribution of clinical and histopathological criteria. Patients with chRCC present with less advanced tumors which leads to better tumor-specific survival rates in general; however, this advantage could not be verified after adjustment for the established risk factors.
