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Plutonic Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
The batholith rocks of California were the source of the gold that sparked the short-lived California gold rush beginning in 1848. Valuable metals, including gold, silver, and copper, can be dissolved from granitoids and concentrated in veins called lodes. The California gold rush started with placer mining—mining of gold from stream deposits (placers) in foothill valleys. The placers were soon exhausted, but miners successfully followed the gold upstream and discovered the Mother Lode—the source of the placer gold—in the Sierra Nevada Mountains. The lode is a zone of veins ranging up to 6 kilometers wide and nearly 200 kilometers long, stretching from the mountains northwest of Sacramento to the foothills southwest of Yosemite National Park. Although placer mining ceased after a few years, following the initial gold rush, the Mother Lode produced significant amounts of gold for about 100 years.
Gold And Silver
Published in Earle A. Ripley, E. Robert Redmann, Adèle A. Crowder, Tara C. Ariano, Catherine A. Corrigan, Robert J. Farmer, L. Moira Jackson, Environmental Effects of Mining, 2018
A. Ripley Earle, Robert E. Redmann, Adèle A. Crowder, Tara C. Ariano, Catherine A. Corrigan, Robert J. Farmer, Earle A. Ripley, E. Robert Redmann, Adèle A. Crowder, Tara C. Ariano, Catherine A. Corrigan, Robert J. Farmer, L. Moira Jackson
No precise data could be found quantifying the overall environmental effects of placer mining. Present operations are many and small. In fact, it is little more than a cottage industry—80% use fewer than six workers and only 5% employ more than nine (LeBarge and Morison 1990)—and, as such, often escapes government inspection. The main environmental effects of placer mining are land disturbance and erosion and the disruption of riverine ecosystems. Subsequent chain effects include stream sedimentation, as well as subsidence and slumping, especially in permafrost areas (French 1976).
Pertinence of alternative fine aggregates for concrete and mortar: a brief review on river sand substitutions
Published in Australian Journal of Civil Engineering, 2022
Branavan Arulmoly, Chaminda Konthesingha
Most studies showed that the contractors are willing to use river sand due to the higher workability of mixes because of the improved particle characteristics (Kwan 2000; Mia, Salman, and Ahmed 2017; Sun et al. 2020). On the other hand, Kwan (Kwan 2000) explains some negative impacts of the deleterious contents of river sand such as clay and silt. The escalated demand for river sand enhances the over-extraction near riverbeds and improper sand processing which allows considerable silt and clay contents without converging to the limitations (Sing, Love, and Tam 2012). Padmalal & Maya (Padmalal and Maya 2014) concluded that river sand extraction is widespread in most developing and developed countries. The authors also mentioned that the fluvial systems (i.e. with a catchment area of lesser than 10,000 km2) of developing countries are highly affected due to increased sand mining. Gavriletea (Gavriletea 2017) and Walker et al (Walker et al. 2016) briefly highlighted the environmental impacts from various river sand mining activities such as deforestation, soil erosion, disruptions to the eco-system, and loss of biodiversity. The authors also stated that placer mining leads to the increased pollution of streams, production of toxic wastewater, erosion of seam banks, and the open-pit mining affects complete eco-system destruction. Pereira & Ratnayake (Pereira and Ratnayake 2013) described some more adverse effects such as lowering of groundwater table and deterioration of water quality due to the degradation of riverbeds and erosion of the banks. Therefore, to overcome such environmental impacts, researchers are now suggesting different alternatives to replace river sand fully or partially in construction works through various laboratory studies.
Gold placer characteristics in marine sediments of Bayah, West Java, Indonesia
Published in Australian Journal of Earth Sciences, 2023
H. Kurnio, Y. Dahlan, J. Kanily
The term ‘placer’ is derived from Spanish, ‘alluvial sand’. Placer deposits form from an accumulation of valuable minerals by gravity separation from a specific source rock during sedimentary processes (Gerhard & Pat, 2006). Gold derived from placer mining was the main source of gold in pre-industrial times. Placer gold, which has a specific gravity greater than 2.58 and resistance to weathering (Gerhard & Pat, 2006), occurs as native Au. The high specific density relates to the hydraulic behaviour that occurs with coarse sediments (Clifton et al., 1967).