Winning Silver

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Date
2013-06-12Author
Moncada de la Rosa, Jorge Daniel
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The search for mineral deposits is a time consuming, risky and very
expensive process. Applying new models and methods provides a competitive
advantage in the search for mineral deposits because an explorationist can
quickly evaluate potential targets and eliminate areas without good potential for
mineralization.
This dissertation presents a practical technique for prediction to finding
precious metal mineralization at Guanajauato mining district (GMD) base on
theoretical and experimental studies of fluids properties, mineral phase
equilibrium, physical and chemical mechanisms. Making the technique highly
transportable so that it can be applied in the field during an exploration program
base on petrographic characteristics of mineral textures produced during boiling
events in quartz, calcite and adularia, and fluid inclusions contained in these
phases. While this work was conducted in GMD, the results should be applicable
in exploration for epithermal deposits worldwide.
The GMD is one of the largest silver producing districts in the world. Ore
shoots are localized along three major northwest trending vein systems, the La
Luz, Veta Madre and Vetas de la Sierra. More than 1200 samples were collected
from surface outcrops, underground mine and historical and recent drill core.
Traverses perpendicular to veins in all system were also conducted. Most of the
samples (approximately 90%) were also assayed for Au, Ag, Cu, Pb, Zn, As, Sb.
Samples from the GMD show a wide range in silica textures are indicative
of rapid precipitation, such as occurs when fluids boil. Other mineral phases,
including illite, rhombic adularia and bladed calcite are also indicative of rapid
growth in a hydrothermal system and are characteristic of boiling systems.
Because boiling is an effective mechanism for precipitating gold and silver from
hydrothermal fluids, the presence of mineral textures indicative of boiling is a
desirable feature in exploration. In many samples, textural evidence for boiling is
supported by coexisting liquid-rich and vapor-rich fluid inclusions, or Fluid
Inclusion Assemblages consisting of only vapor-rich inclusions, suggesting
"flashing" of the hydrothermal fluids. Textural and fluid inclusion evidence for
boiling has been observed in the deepest levels of the GMD, suggesting that
additional precious metal resources may occur beneath these levels.
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- Doctoral Dissertations [13025]