Christina

Mine, Active?

Alternative names

Vetter
Shelden

Commodities and mineralogy

Main commodities Au
Other commodities Ag; Sb
Ore minerals gold; stibnite

Geographic location

Quadrangle map, 1:250,000-scale LG
Quadrangle map, 1:63,360-scale A-1
Latitude 65.069
Longitude -147.378
Nearby scientific data Find additional scientific data near this location
Location and accuracy Cobb (1972), loc. 43; SE1/4 section 20, T. 3 N., R. 2 E., of the Fairbanks Meridian. This deposit is on the divide separating Chatham Creek and Wolf Creek. The location accuracy is within 2,000 feet. It is located within the Golden Summit Project area.

Geologic setting

Geologic description

In the 1950s through the 1970s, almost 20,000 ounces of gold was mined from surface and underground workings on the Christina prospect. Exploration continued throughout the 1980s, when several holes were drilled to explore the extent of mineralization in the Christina system. Based on the drilling conducted in the 1980s, reserves have been estimated at over 68,000 ounces of gold. Mineralization is characterized as schist-hosted auriferous shear systems with discrete and/or crushed veins and skarn.
The following geologic description is based on mapping conducted by Fairbanks Exploration Inc. (unpublished report, 1988): The Christina prospect consists of a N 70-80 W, 75 S shear zone. The Christina shear separates Cleary sequence rocks to the north from Fairbanks Schist to the south. The Cleary sequence forms the footwall and consists of interbedded rhyolite metatuff, laminated graphitic quartzite, black graphitic schist and chloritic calc-schist. The hanging wall is composed of biotite-quartz-mica schist, and micaceous quartzite. Both the hanging wall and foot wall are gently folded into east-west trending open folds whose axes plunge 10 to 20 degrees to the west. Amplitudes of the open folds range from 4 to 8 feet and wavelengths range from approximately 10 to 40 feet.
On an outcrop scale, the Christina structure contains a series of parallel quartz veinlets which pinch and swell and form a sinuous outcrop pattern along strike (Freeman and others, 1998). For example, the Christina shear on the west end consists of two discrete, quartz-rich zones with a total thickness of approximately 2 feet. Within 60 feet of strike length to the east, the quartz-rich zones merge and pinch down to a thickness of a few inches. In general, the Christina shear contains less massive quartz and more stockwork quartz to the east.
Hypogene and supergene alteration of the shear and adjacent wallrock has produced reddish hematite after pyrite, greenish scorodite after arsenopyrite, and yellow to white antimony oxides after stibnite, jamesonite and boulangerite. Sulfide and oxide alteration typically form envelopes paralleling the shear. Alteration in the footwall reaches at least 40 feet from the shear in the lower sample area near the Vetter shaft while alteration in the hanging wall is minor. Scorodite and hematite alteration were most prevalent in the western portion of sample area. Antimony oxide alteration becomes pervasive in the central portion of the vein where quartz-free pods of massive, striated stibnite occur.
In 1981, Placid Oil Company completed 4661 feet of diamond drilling in 16 holes on the Christina and Orange Free shear zones. The Orange Free shear zone has a northeast strike nearly perpendicular to the Christina shear zone. In 1985, Placid Oil utilized reverse circulation rotary drilling techniques to complete 4623 feet of drilling in 18 holes on the Christina shear zone. At a 5-foot mining width, the Christina system had drill indicated reserves of 39,600 tons grading 0.660 ounces of gold per ton and 1.74 ounces of silver per ton in one block; another block containing 73,900 tons grading 0.370 ounce of gold per ton and 0.71 ounce of silver per ton. The Spirit shear zone, located in the hanging wall of the Christina shear zone, contained an estimated reserve of 36,900 tons grading 0.411 ounce of gold per ton and 0.40 ounce of silver per ton over a five-foot mining width (Porterfield and Croff, 1986). The average grade of the Christina shear zone was 0.551 ounce of gold per ton and 0.61 ounce of silver per ton while the Orange Free shear zone averaged 0.167 ounce of gold per ton and 15.4 ounces of silver per ton (Bentzen, 1982).
Geologic map unit (-147.380448444367, 65.0685776474247)
Mineral deposit model Polymetallic veins (Cox and Singer, 1986; model 22c)
Mineral deposit model number 22c
Age of mineralization Probably about 90 Ma based on analogy with similar gold deposits nearby (Freeman, 2008).
Alteration of deposit Hypogene and supergene alteration of the shear and adjacent wallrock has produced reddish hematite after pyrite, greenish scorodite after arsenopyrite, and yellow to white antimony oxides after stibnite, jamesonite and boulangerite. Sulfide and oxide alteration typically form envelopes paralleling the shear. Alteration in the footwall reaches at least 40 feet from the shear near the Vetter shaft while alteration in the hanging wall is minor. Scorodite and hematite alteration were most prevalent in the western portion of the deposit. Antimony oxide alteration becomes pervasive in the central portion where quartz-free pods of massive, striated stibnite occur (Fairbanks Exploration Inc., unpublished report, 1988).

Production and reserves

Workings or exploration
Mineralization on the Kawalita claim, which adjoins the Christina prospect to the south and east, was discovered in 1908 (Smith, 1913). Between 1961 and 1963, Ed Ebbert sank an inclined shaft to a depth of 50 feet on the western end of the Kawalita claim. In 1963, this shaft was deepened to 147 feet and the haulage levels moved into the footwall to better control the heavy ground and water. The underground portion of the mine was closed in 1965, but surface mining on the Kawalita claim continued through 1966.
In late 1977, Tri-Con Mining and Mohawk Oil Company extracted shear zone material from surface cuts on the Christina claim over a strike length of 450 feet to a depth of 15 feet. In early 1978, Placid Oil Company leased the Christina prospect and began an extensive exploration and development program. Geological mapping, VLF and magnetics geophysical surveys, and soil and rock geochemical sampling surveys were followed up in 1978 with dozer trenching and completion of 5174 feet of diamond core drilling in 23 holes. Approximately 2314 feet of diamond core drilling in nine holes as well as extensive soil grid geochemical surveys were completed in 1980 on the Christina shear zone system. In 1981, approximately 1489 feet of trackless underground drifting was driven to and on the Christina shear zone system. The Christina adit was constructed at a design size of 8 feet by 8 feet, however, timbering in some areas reduced the finished dimensions of the workings. During construction of the adit a previously undiscovered shear zone, the Orange Free shear zone, was intersected approximately 300 feet from the portal. In addition to the underground workings, Placid Oil completed 4661 feet of diamond drilling in 16 holes on the Christina and Orange Free shear zone.
Activities on the Christina in 1982 consisted of 13,045 feet of diamond core drilling in 25 holes designed to test the down-dip extension of the Christina system. In addition, 600 pound bulk samples were collected by Placid Oil Company from the Christina shear zone and the Orange Free shear zone where these shears were exposed in underground workings (Bentzen, 1982). Activities on the Christina prospect in 1983 consisted of 8512 feet of diamond core drilling in 23 holes to further outline ore shoots on the Christina shear zone (Porterfield and Croff, 1986). In 1985 Placid Oil utilized reverse circulation rotary drilling techniques to complete 4623 feet of drilling in 18 holes on the Christina shear zone. In 1986, Fairbanks Exploration Inc. conducted preliminary grab sampling of the Christina adit and Nordale adit dumps (Fairbanks Exploration Inc., unpublished report, 1986).
During July, 1988, Fairbanks Exploration Inc. extracted a bulk sample from a high grade portion of the Christina shear zone in the same area as the 1986 bulk sample and the Mohawk open cut. Initial work on the program entailed stripping overburden to prepare a 12 foot wide pad along the length of the shear zone. Ore was extracted with a backhoe by digging a trough approximately 3 feet wide and 3 feet deep. After each three-foot lift was mined, the footwall and hangingwall were stripped to expose the next lower bench for mining. Two separate areas on the Christina prospect were mined to obtain the 1988 bulk sample. Most of the tonnage (approximately 85 percent) was excavated from the upper sample area; the remaining 15 percent of the ore was extracted from the lower sample area.
During the summer and fall of 1990, Polar Mining conducted bulk sampling of the Christina shear zone near the Kawalita shaft. Unlike the Christina shear in the 1988 bulk sample area, the Polar Mining sample area contains mineralization in both the foot wall and hanging wall of the Christina shear. Polar Mining exposed this shear zone for approximately 500 strike feet. Approximately 1,000 to 1,200 tons of material were extracted from this area and treated in a one stage wet jig. This method of sampling proved unsatisfactory since tailings ponds averaged 0.14 ounce of gold per ton (P. Metz, oral communication, 1991) while the recovered grades averaged 0.030 to 0.033 ounce of gold per ton (D. May, oral communication, 1990).
From 2011 to 2012, Freegold Ventures Ltd. undertook its first drilling in the Christina area, completing 12 holes. In 2011, an induced polarization (IP) and resistivity survey was executed. In 2012, ground based geophysics and shovel soil sampling was conducted. (Abrams and Giroux, 2013).
Indication of production Yes; small
Reserve estimates None.
Production notes
Between 1957 and 1961, approximately 4900 troy ounces of gold was extracted from 500 feet of surface strike on the Kawalita claim (R. Vetter, oral commun., 1991; Saunders, 1960, ATDM MR 49-4). The shear zone material averaged one troy ounce per ton (Brown, 1962; R. Vetter, 1986, oral commun.). Between 1961 and 1966, an estimated 10,000 ounces of gold was extracted from surface and underground workings on the Christina prospect on the Kawalita claim (R. Vetter, oral commun.1986). In 1963 and 1964, Scott Haskins extracted 962 troy ounces of gold from shear zone material which averaged 1.96 ounces per ton over 350 feet of strike to a depth of 10 feet (S. Haskins, 1986, oral commun.). Mr. Haskins also sunk a 90 foot shaft on the shear zone but production from this shaft was insignificant. In 1967 and 1968 approximately 250 troy ounces of gold was extracted from a 35-foot-deep shaft and 110 feet of surface workings (R. Vetter, oral commun., 1986). In late 1977, Tri-Con Mining and Mohawk Oil Company leased the Christina claim and extracted shear zone material from surface cuts over a strike length of 450 feet to a depth of 15 feet. Material from this open cut averaged approximately 3 troy ounces of gold per ton (R. Vetter, oral commun., 1986). Total production by Tri-Con-Mohawk is estimated at 3375 troy ounces of gold.
Prior to World War II, 20,000 ounces of gold were mined from Christina (Abrams and Giroux, 2013).

References

MRDS Number A015443

References

Bentzen, E.H., 1982, Summary and conclusions of metallurgical test, Christina vein, Cleary Summit project, Alaska: Colorado School of Mines Research Institute unpublished report to Placid Oil Company, 11 p.
Brown, J.M., 1962, Bedrock geology and ore deposits of the Pedro Dome area, Fairbanks Mining District, Alaska: Fairbanks, University of Alaska M.S. thesis, 137 p.
Freeman, C.J., 2008, Executive summary report for the Golden Summit project, Fairbanks Mining District, Alaska: Unpublished Technical Report for Freegold Ventures Ltd., 112 p. (posted on www.sedar.com, March 31, 2008) http://www.sedar.com/GetFile.do?lang=EN&docClass=24&issuerNo=00004004&fileName=/csfsprod/data88/filings/01242796/00000001/k%3A%5CSedar%5Cfilings%5Clivework%5Cwkout%5C19016%5CCS_tech.pdf (as of December 23, 2014).
Freeman, C.J., Flanigan, B., Currey, J., Wolf, K., and Wietchy D.W., 1998, 1997 and 1998 Final report, Golden Summit project, Fairbanks mining district, Alaska: Avalon Development Corp. Geologic Report GS98-1, 37 p. (Report held by Freegold Recovery Inc. USA, Vancouver, British Columbia.)
Porterfield, J. and Croff, C., 1986, Summary report for the Cleary Project, Fairbanks district, Alaska - 1985: Placid Oil Company report, 36 p.
Reporters C.J. Freeman, J.R. Guidetti Schaefer (Avalon Development Corporation); V.C. Zinno (Alaska Earth Sciences, Inc.)
Last report date 12/23/2014