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2 Geology and Geochemistry of Gold Occurrences in Virginia
Pages 23-46

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From page 23...
... described ore deposits in the Virgilina district that spans the Virginia–North Carolina border. This chapter is necessarily a condensed and simplified summary of Virginia geology and its known gold occurrences.
From page 24...
... Some prospects and small deposits occur in the Blue Ridge province, but no lode deposits are known to occur in the Valley and Ridge or Appalachian Plateau provinces. Gold deposits may exist in buried Piedmont rocks that extend beneath the Coastal Plain sediments, but this region has not been explored.
From page 25...
... The Eastern Piedmont consists of multiple terranes, with the Carolina Terrane that includes a northern extension of the Carolina Slate Belt (Hackley et al., 2007) and hosts the Virgilina district gold deposits, being most relevant to this report.
From page 26...
... BOX 2-1 Sulfide Minerals in Virginia Metals of economic importance in ore deposits are often hosted in sulfide minerals. Sulfides that have been identi fied in both massive sulfide deposits and in quartz-gold veins in Virginia and which are most relevant to this report include • Iron sulfides: pyrite (FeS2)
From page 27...
... Given the close association between the two deposit types, it has been proposed that the low-sulfide goldquartz veins and the massive sulfide deposits have a similar origin. Lonsdale (1927)
From page 28...
... . In the northern part, the gold deposits occur to the west of the massive sulfide deposits and are hosted in Potomac Terrane rocks, whereas in the central and southern part of the trend the gold deposits are intermingled or to the east of massive sulfide deposits and are hosted in Chopawamsic-Quantico rocks.
From page 29...
... GEOLOGY AND GEOCHEMISTRY OF GOLD OCCURRENCES IN VIRGINIA 29 FIGURE 2-4  Location of selected deposits in the Mineral district, color-coded according to deposit type. Gold, base metal, and pyrite deposits are intermingled in this section of Virginia.
From page 30...
... report that no massive sulfide ore bodies (such as those that are common in the gold-pyrite belt) are present in the Virgilina district.
From page 31...
... Thus, in order to characterize Virginia's gold deposits and compare them with those found elsewhere, it is useful to consider the geologic history of Virginia's gold deposits, including both the original environment in which the gold was formed and how it has been modified over time. Evidence suggests that most of the gold in Virginia's gold-pyrite belt and Virgilina district was originally deposited in submarine volcanic massive sulfide deposits or submarine equivalents of subaerial epithermal deposits, and subsequently remobilized during later metamorphism and deformation to form low-sulfide, gold-quartz vein deposits.
From page 32...
... This complex geologic and tectonic history means that at the regional scale Virginia gold deposits occur along shear zones that extend for tens of kilometers, whereas at the local or mine scale mineralization is most closely associated with later faults, especially in the more broken areas where the shear zones are crossed by tension cracks.
From page 33...
... . FIGURE 2-7  Sketch showing a larger quartz vein (lower right)
From page 34...
... . Descriptions of the Franklin Mine in Fauquier County illustrate the pinch-and-swell nature of the gold-quartz veins.
From page 35...
... The fixed price of gold from 1834 to 1933 was $20.67 per ounce; therefore, the reported gold production in dollars corresponds to about 160,000 ounces of gold produced in Virginia over a 105-year period. For comparison, the Turquoise Ridge Gold Mine in Nevada produced 287,144 ounces of gold in 2020, the Carlin trend gold mines in Nevada (which include the Arturo JV, Betze Post, Carlin Trend Operations, and Meikle mines)
From page 36...
... For comparison, in 2021 the Haile Mine in South Carolina produced 3,214,000 tons of ore, an amount estimated to exceed the total amount of ore produced in the more than 100-year history of gold mining in Virginia. Thus, while gold grades being mined in the 1800s and early 1900s in Virginia were comparable to grades being mined elsewhere in the United States today, the total ore tonnage mined at the Virginia gold mines was small compared to most mines operating in the United States today.
From page 37...
... This observation agrees with the committee's study of drill cores from the Vaucluse Mine to Virginia Energy in Charlottesville on March 30, 2022, as well as the committee trip to the exploration property of Aston Bay Holdings, Ltd., on April 28, 2022. Nevertheless, as discussed above, the gold-quartz veins can be in close proximity to massive sulfide deposits, which may have >90 percent pyrite.
From page 38...
... As such, mining of these volcanogenic massive sulfide deposits can lead to significant acid rock drainage and elevated metal contents in waters that traverse the mine site. Data reported from the Greenwood Mine low-sulfide, gold-quartz vein deposit (Prince William County)
From page 39...
... . While neither the Cabin Branch nor the Valzinco massive sulfide deposits produced gold, the much higher concentrations of some elements of interest in massive sulfide deposits compared to gold-quartz veins illustrates the potential impact that massive sulfides could have on water quality should one of these bodies be intentionally or unintentionally disturbed during mining to access the gold-quartz veins.
From page 40...
... Massive sulfide Valzinco (sample 99VLZN9) 0.13 62 160 15,000 260 4.2 33 <2 69,000 deposit Valzinco tailings 1.6–8.6 19–46 0.4–110 280–2,000 2,400–16,000 5.5–21 -- 0.75–1.9 230–21,000 Cabin Branch (sample CB-ORE-1)
From page 41...
... (mg/L) VA Surface Water Quality Criteria (9 VAC -- -- 0.01 0.005 1.3 0.015 0.0056 0.17 0.00024 7.4 25-260-140)
From page 42...
... The committee views the concentrations measured in water samples at the Greenwood Mine as reflective of a scenario in which only the low-sulfide, gold-quartz vein and adjacent wallrock are disturbed during gold mining in Virginia. Owing to the close spatial relationship of the gold-quartz vein deposits with massive sulfide deposits in the gold-pyrite belt, it is possible that some sulfide-rich material could be intersected and disturbed during mining of the low-sulfide, gold-quartz vein deposits.
From page 43...
... Massive Sulfide Deposits Comments Al As Cd Cu Pb Sb Se Tl Zn Sample (sample name)
From page 44...
... The Haile Gold Mine, for example, consists of numerous quartz veins or lenses with disseminated gold, producing ore bodies that are wider and larger than those in Virginia (OceanaGold, 2022b; see Figure 2-11)
From page 45...
... . As noted above, Virginia low-sulfide, gold-quartz vein deposits are found in close association with massive sulfide deposits (gold-pyrite belt)
From page 46...
... As demonstrated by the London and Virginia, Buckingham, and Williams Mines, massive sulfide bodies can occur in close proximity to gold-quartz vein deposits in Virginia, and could release acid rock drainage and metals if disturbed during mining. The rocks surrounding the known gold deposits are composed of common rock-forming minerals, which are unlikely to release significant amounts of harmful metals or compounds to the environment, even in the presence of ARD.


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