The Batopilas Mining District was a major silver producer, with estimated historic production of more than 300 million ounces. Orebodies consist of high-grade silver in the forms of native silver, acanthite and proustite hosted dominantly in calcite veins. Recent exploration has facilitated the reexamination of the geologic features and origin of the enigmatic native silver district. Sulfur, lead, and strontium isotopic studies have been conducted to constrain the fluid and metal sourcing. [delta]³⁴SvCDT isotope signatures for galena, sphalerite and pyrite range from -8 to -2, -6 to 0, and -5 to 3°/₀₀, respectively. A fractionation temperature of 227±25 °C can be obtained using average sulfur isotope values for galena and sphalerite. Galena lead isotopic values show two distinct signatures. Samples of massive-replacement style mineralization have ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb values of 18.742 and 18.747, 15.611 and 15.618, and 38.512 and 38.535, respectively. For vein samples, the corresponding values range from 18.799 to 18.817, 15.623 to 15.639, and 38.603 to 38.655. The lead isotopic signatures for vein galena have lower thorogenic lead content than other ore deposits in the Sierra Madre Occidental, suggesting a different source of metals. Vein calcite samples have ⁸⁷Sr/⁸⁶Sr isotopic compositions ranging from 0.707551 to 0.70590 (±0.000009) and Sr concentrations ranging from 51 to 246 ppm. These vein components may reflect mixed deep-marine sedimentary and Precambrian basement sources. A reconnaissance fluid inclusion study was conducted to better constrain fluid temperature and composition. The minerals studied included quartz, fluorite, and two types of sphalerite. The average eutectic temperatures obtained are -38°C, -31°C, and -43°C, respectively, indicating a complex mineralizing brine. Homogenization temperatures averaged 143°C, 165°C, and 174°C, and the NaCl equivalent weight percents averaged 4, 7, and 17, respectively. Fluids involved in vein mineralization are different from those typical of epithermal vein Ag-Au deposits, and may represent sedimentary brines that have circulated through the underlying basement. / text

The Viking Age (800–1050 A.D.) is also called the “Silver Age”. Despite the fact that no silver mines were in use in Sweden at that time, most of the landowners for one reason or another had a lot of precious metal stored in their homes. Alone the Island of Gotland has found over 700 different hoards of which around 400 of these hoards have been excavated over the last 100 years. Archeologists are debating whether all this precious metal had been brought to the island by traders from the east, or if it came from the Viking raids in the west. Besides the coins, thousands of pieces of silver have been recorded. The intention of this essay is to attempt to clarify if it is possible to find differentiating factors between the hoards and to classify categories of these precious metal deposits. I indeed, such classifications and categorizations are achievable in the research findings in this paper.

The purpose with this work is to try and see an economic development on Gotland during the Viking Age, where society went from a weight-based economy, to a monetary economy with its own coins. The aim is to try and distinguish a pattern in the investigated depots. How has the deposit structure changed during the Viking era when it comes to the minted and unminted silver?   The research about the silver deposits aim on the dating of the coins in order to create an approximate closing period for the contents of the depots.   The development of the silver structural change in the silver depots during the Viking Age makes it possible to study how the dominance of the early Islamic coins, in both coin and fragmented form, is phased out to be replaced by mainly English and German coins. The English and German coins that are found on Gotland could be seen as a model for the coins and the minting that began at the end of the Viking Age on the island.

Exploration companies commonly rely on geochemistry to identify alteration of distinctive geochemical and mineralogical character, surrounding metal sulphide deposits that were precipitated from hydrothermal fluids. However, examination of raw analytical data is prone to error due to closure effects and the difficulty in removing the effects of background variation in unaltered rocks from the variations imposed by later hydrothermal alteration. Closure can be avoided by using ratios, or by utilising mass balance approaches based on fixing volume, mass or concentration changes between samples of parent and daughter lithologies. Using a parent-daughter approach is limiting, because only pairs of samples can be compared at any one time and because an unaltered equivalent must be produced for each sample examined in this way. Pearce Element Ratio analysis and General Element Ratio analysis (PER and GER) are not restricted in this fashion, and are more amenable to interrogation of large data sets. PER and GER are also capable of decoupling background variation from that variation due to hydrothermal alteration. Furthermore, these ratio methods are readily applied to commercially derived lithogeochemical assays. In this study, various analytical methods and interpretive techniques (including PER and GER) have been applied to identify alteration in rocks around the Century and Elura Zn-Pb-Ag deposits, and to assess whether primary ore-related alteration effects can still be identified once altered rocks have been subjected to weathering. Ratios of trace elements over a conserved element have been used to generate a suite of pathfinder elements for each deposit. Elements enriched in host rocks around both deposits include the economic metals Zn, Pb and Ag, along with Rb and Tl. Sodium is ubiquitously depleted in altered rocks. Other elements in the pathfinder suites are distinctive to each deposit type, and include a number of major and trace elements that are added or removed from the rocks around the mineralised zones. For example, Sb and As are enriched in rocks around Elura mineralisation while Ge and Cd are enriched in samples around Century deposit. Iron carbonate development accompanied by potassic alteration, the destruction of albite and the absence of chlorite are the dominant mineral alteration effects at both deposits. PER and GER diagrams have been used to quantify the intensity of this alteration and allow lithogeochemistry to be used to vector towards high intensity alteration, which is adjacent to Century and Elura mineralisation. These ratio methods are applied to both visibly and cryptically altered rocks at both deposits, and have a very high degree of success in classifying alteration in unweathered rocks. The following simple PER ratios indicate proximity to Elura mineralisation: Ca/C, K/Al for shales, K/(Al-Na) for siltstones/sandstones. The following simple PER ratios indicate proximity to Century mineralisation: Mn/Ti, Mg/Ti and Fe/Ti vs C/Ti, K/Ti vs Al/Ti, K/Ti vs (Al-Na)/Ti. Pathfinder elements can be overlain onto PER and GER diagrams to aid in ranking the prospectivity of samples, and to assess mineral hosts for individual pathfinder elements. Weathering destroys most indicators of alteration in the Elura area, while alteration signatures are better preserved in host rocks around the Century deposit.