Greens Creek

Mine, Active

Commodities and mineralogy

Main commodities Ag; Au; Cu; Pb; Zn
Other commodities Ba; Bi
Ore minerals acanthite; barite; bornite; chalcopyrite; electrum; freibergite; galena; proustite; pyrite; sphalerite; tetrahedrite; tennantite-tetrahedrite
Gangue minerals calcite; graphite; quartz

Geographic location

Quadrangle map, 1:250,000-scale JU
Quadrangle map, 1:63,360-scale A-2
Latitude 58.079
Longitude -134.6312
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Greens Creek Mine is at an elevation of 1,500 feet on the south side of Greens Creek on Admiralty Island. The mine is marked on the Juneau A-2 topographic map in the NW1/4 section 9, T. 44 S., R. 66 E. of the Copper River Meridian. The location is accurate to about 1/4 mile.

Geologic setting

Geologic description

The Greens Creek deposit is discontinuous along the contact between a structural hanging wall of thinly laminated, quartz-mica-carbonate phyllite and a structural footwall of black, graphitic, meta-argillite. Fossils in calcareous, black argillite clasts in pyritic massive sulfide ore are Late Triassic in age (Crafford, 1989). The most intense alteration is closest to the copper-rich portions of the orebody and consists of intense silica-pyrite alteration. Three main types of ore have been recognized at the Greens Creek Mine: massive, black, and white. Massive ore is the most common and contains more than 50 percent sulfides, chiefly pyrite, sphalerite and galena, in a matrix of locally barite-bearing silica-carbonate rock. Less-abundant ore minerals include chalcopyrite, tetrahedrite, freibergite, proustite, and electrum. The pyrite content of the massive ore varies from 80 to 90 percent in base-metal-poor ore to 10 to 15 percent in base-metal-rich ore. The black ore is similar to the massive ore, except that it contains appreciable graphite. White ore varies depending upon whether the gangue is primarily barite, silicates, or carbonates. The white ore is pyrite-poor and contains coarse-grained tetrahedrite-tennantite, bornite, freibergite, proustite, galena, sphalerite, chalcopyrite and acanthite. Very high precious metal values are common in base-metal-rich massive sulfides near the stratigraphic hanging wall contact, but gold is common in all three types of ore (Newberry and others, 1997).
The Greens Creek deposit was discovered in 1973 by following up a zinc stream-sediment anomaly (T.C. Crafford, oral communication, 2000). The underground mine and concentrator facility began operation in 1989, but was placed on standby in 1993, followed by a $114-million, 3-year, modernization. Operations resumed in 1996 (Kennecott Minerals Company, 2001) and have continued steadily to 2011. The deposit is serviced by 13 miles of road. In addition to the mine, there is an ore concentrating mill, a tailings impoundment area, a ship-loading facility, camp facilities, and a ferry dock at Hawk Inlet. Ore from the underground trackless mine is milled at the mine site. The mill produces gold-silver dore as well as lead, zinc and bulk concentrates. Concentrates are shipped from a marine terminal about nine miles from the mine site.
The rocks in the surrounding area are mainly Ordovician and Devonian to Triassic, clastic units, mafic-intermediate volcanic rocks, and subordinate limestone. The bedded rocks are intruded and locally metamorphosed by Cretaceous granodiorite (Gehrels and Berg, 1994).
In 2008, Hecla Mining Company acquired a 100 percent interest in the mine from Rio Tinto (Hecla Mining Company, 2011). In 2009, the Greens Creek Mine produced 7,459,170 ounces of silver, 67,278 ounces of gold, 70,379 tons of zinc, and 22,254 tons of lead from 790,871 tons of ore that was milled (Szumigala and others, 2010). In 2009, 39,000 feet of infill and exploration drilling added ore reserves equivalent to the ore that was mined that year. In 2009, the proven and probable ore reserves were 8,314,700 tons with an average grade of 12.1 ounces of silver per ton, 0.10 ounce of gold per ton, 20.3 percent zinc, and 3.6 percent lead.
In 2012, the Greens Creek Mine produced 1) 6,400,000 ounces of silver, 2) 55,496 ounces of gold, 3) 64, 249 tons of zinc, and 21,074 tons of lead from 789,569 tons of ore that was milled (Athey and others, 2013). In 2012, the proven and probable ore reserves were reported as 1) 92,500,000 ounces of silver with an average grade of 11.9 ounces of silver per ton, 2) 713,000 ounces of gold with an average grade of 0.09 ounces of gold per ton, 3) 9.0 percent zinc, and 4) 3.4 percent lead (McDonald and others, 2013).
In 2016, Hecla Mining Company produced 9,253,543 ounces of silver from Greens Creek mine, which was the highest since Hecla acquired 100 percent of the mine in 2008, an increase over the prior year by 9.5 percent; gold production of 53,912 ounces decreased by 11.0 percent from the 2015 level. The mine also yielded 20,596 tons of lead, and 57,729 tons of zinc. The mill operated at an average of 2,229 tons per day for the year, for a total of 815,639 tons. Ore grades milled were 14.55 ounces of silver per ton, 0.10 ounce of gold per ton, 3.11 percent lead, and 8.08 percent zinc. Definition drilling at Greens Creek in 2016 refined the resources of the 9A, Southwest Bench, East Ore and NWW zones (Athey and Werdon, 2017).
Geologic map unit (-134.632978077925, 58.0786650132543)
Mineral deposit model Kuroko massive sulfide deposit (Cox and Singer, 1986; model 28a).
Mineral deposit model number 28a
Age of mineralization Fossils in calcareous, black argillite clasts intercalated with pyritic massive-sulfide ore are Late Triassic (Crafford, 1989).
Alteration of deposit The most intense alteration is closest to the copper-rich portions of the orebody and consists of intense silica-pyrite alteration.

Production and reserves

Workings or exploration
The Greens Creek deposit was discovered in 1973. The underground mine and concentrator began operation in 1989. The deposit is serviced by 13 miles of road. In addition to the mine, there is an ore concentrating mill, a tailings impoundment area, a ship-loading facility, camp facilities, and a ferry dock at Hawk Inlet. The mine has been in continuous operation since 1996 after a few year's interruption to modernize the plant. In 2008, Hecla Mining Company acquired a 100 percent interest in the mine from Rio Tinto. In 2009, 39,000 feet of infill and exploration drilling added ore reserves equivalent to the ore that was mined that year.
Exploration at Greens Creek mine is concentrated along the trend of numerous underground volcanogenic massive sulfide ore bodies, and on Hecla Mining Company’s 23-square-mile, surface land package. Exploration work in 2016 increased reserves for the 9A and NWW zones, where approximately 8.3 million ounces of silver and 46,500 ounces of gold were added. Measured and indicated resources were increased with additions in the 9A, NWW, SW, Gallagher zones, and the newly established Upper Plate resource. Inferred resources decreased for silver and gold overall, as they were converted to reserves and indicated resources at the NWW Zone; all other zones, except 200 South, showed increases in inferred gold and silver resources.
In 2016, exploration drilling was concentrated on the Gallagher Zone and the Mine Syncline, a new exploration target area where the ore horizon has been identified in the north and south-central parts of the mine. Drilling of the NWW Zone’s southern extension continues to define mineralization along the lower fold, continuing from the fold nose and along the upper limb. Mineralization is represented by multiple distinct bands of massive ore and mineralized argillites and has similar geometry and dimensions to the current resource model. Highlights of assay results include 45.4 ounces of silver per ton, 0.20 ounce of gold per ton, 19.0 percent zinc, and 10.3 percent lead over 18.6 feet, and 51.7 ounces of silver per ton, 0.20 ounce of gold per ton, 11.2 percent zinc, and 4.8 percent lead over 10.0 feet. Drilling also targeted the Upper Southwest Zone around previously mined levels, and identified mineralization that extends down to the upper limb of NWW Zone. Highlighted assay results from Upper Southwest Zone include 46.8 ounces of silver per ton, 0.03 ounce of gold per ton, 10.9 percent zinc, and 6.1 percent lead over 10.2 feet. The drilling also identified shallow mineralization east of the Kahuna fault. Recent drilling of the lower 9A Zone has generally confirmed and upgraded the resource model. Initial definition drilling of the East Ore Zone shows that overall the mineralization is thinner than expected compared to the model, but this drilling is advancing into stronger mineralized portions of the resource.
Gallagher Zone exploration drilling targeted a new flat-lying zone above the 4211 Drift that may define an ore-horizon contact that steepens to the east near the Gallagher fault. Deep exploration drilling of the Mine Syncline shows the ore-horizon contact continues steeply down dip from the NWW Zone and could define a broad syncline below the current mine infrastructure that could host mineralization. Drilling of this same syncline in the central part of the mine shows the ore-horizon contact is the down-dip extension of the lower fold limb of the NWW zone (Athey and Werdon, 2017).
Indication of production Yes; large
Reserve estimates
In 2009, the proven and probable ore reserves were 8,314,700 tons of of material with an average grade of 12.1 ounces of silver per ton, 0.10 ounces of gold per ton, 20.3 percent zinc, and 3.6 percent lead. In 2009, 39,000 feet of infill and exploration drilling added ore reserves equivalent to the ore that was mined that year.
In 2012, the proven and probable ore reserves were reported as 92,500,000 ounces of silver with an average grade of 11.9 ounces of silver per ton, 713,000 ounces of gold with an average grade of 0.09 ounces of gold per ton, 9.0 percent zinc, and 3.4 percent lead (McDonald and others, 2013).
As of December 31, 2016, proven and probable reserves at Greens Creek include 7.594 million short tons grading 11.7 ounces of silver per ton, 0.09 ounce of gold per ton, 2.9 percent lead and 7.6 percent zinc, for a contained metal content of 88.87 million ounces of silver, 673,000 ounces of gold, 217,280 tons of lead, and 576,130 tons of zinc. Indicated resources include 1,785,000 tons of material grading 10.8 ounces of silver per ton, 0.09 ounce of gold per ton, 3.1 percent lead and 7.8 percent zinc, for a contained metal content of 19.3 million ounces of silver, 154,000 ounces of gold, 55,980 tons of lead, and 139,660 tons of zinc. Inferred resources include 3,397,000 tons of material grading 11.9 ounces of silver per ton, 0.08 ounce of gold per ton, 2.9 percent lead, and 7.2 percent zinc, for a contained metal content of 40.25 million ounces of silver, 285,000 ounces of gold, 98,380 tons of lead, and 243,220 tons of zinc. The total silver resource in all categories is over 148 million ounces (Hecla Mining Company, 2017).
Production notes
In 2009, the Greens Creek Mine produced 7,459,170 ounces of silver, 67,278 ounces of gold, 70,379 tons of zinc, and 22,254 tons of lead from 790,871 tons of ore that was milled (Szumigala and others, 2010).
In 2012, the Greens Creek Mine produced 1) 6,400,000 ounces of silver, 2) 55,496 ounces of gold, 3) 64, 249 tons of zinc, and 21,074 tons of lead from 789,569 tons of ore that was milled (Athey and others, 2013).
In 2016, Hecla Mining Company produced 9,253,543 ounces of silver from Greens Creek mine, which was the highest since Hecla acquired 100 percent of the mine in 2008, an increase over the prior year by 9.5 percent; gold production of 53,912 ounces decreased by 11.0 percent from the 2015 level. The mine also yielded 20,596 tons of lead, and 57,729 tons of zinc. The mill operated at an average of 2,229 tons per day for the year, for a total of 815,639 tons. Ore grades milled were 14.55 ounces of silver per ton, 0.10 ounce of gold per ton, 3.11 percent lead, and 8.08 percent zinc. Definition drilling at Greens Creek in 2016 refined the resources of the 9A, Southwest Bench, East Ore and NWW zones (Athey and Werdon, 2017).

References

MRDS Number A010663; A012083

References

Reporters J.C. Barnett and L.D. Miller (Juneau, Alaska ); D.J. Grybeck (Contractor, USGS); V.C. Zinno (Alaska Earth Sciences, Inc.); M.B. Werdon (DGGS)
Last report date 8/26/2017