Henderson

The Henderson mine, located near Empire, Colorado, is situated in a stunningly beautiful area surrounded by snow-capped peaks and outdoor recreation facilities in Colorado's Rocky Mountains. Climax Molybdenum Company, a subsidiary of Phelps Dodge Corporation with corporate headquarters in Phoenix, Arizona, owns the Henderson Mine. Phelps Dodge is one of the largest mining companies in the world, and is primarily engaged in the production of copper and molybdenum from large open pit mines. The Henderson mine, which produces molybdenum ore by an underground mining method known as panel caving, is the company's only underground operation. Molybdenum is a grayish colored metal that is mainly used to produce high strength alloy steels. Other uses include chemicals and lubricants, and as lament supports in light bulbs. The mine site is located 80.5 km (50 mi) west of Denver, Colorado and lies 3170 m (10,400 ft) above sea level on the eastern side of the Continental Divide. It can easily be reached from Denver International Airport (DIA) by taking Interstate 70 west to the Empire exit, Highway 40 approximately 16 km (10 mi) to the bottom of Berthoud Pass, and continuing approximately 3 km (2 mi) on the well maintained mine access road. The entire trip from DIA can be made in approximately 1.5 hours. The mine site is within Clear Creek County and is surrounded by the Arapaho National Forest. The approximately 11.7 km2 (2900 acre) of land containing the Henderson orebody, located underneath Red Mountain, is entirely privately owned by Climax Molybdenum Company. Additionally, the 52- km2 (12,800 acre) mill site located near Kremmling Colorado is also entirely owned by the company. The mine is currently producing about 21,000 tons of raw ore per day. It is estimated that the mine has adequate reserves for about twenty more years of production. Upon closure of the Henderson Mine, the company plans to re-open the Climax Molybdenum Mine located near Leadville, Colorado.

The Henderson deposit is composed of two partially overlapping ore bodies that lie 1,080 m (3550 ft) beneath the summit of Red Mountain. The ore bodies are entirely within a Tertiary rhyolite porphyry intrusive complex that has intruded the Precambrian Silver Plume granite. The deposit is elliptical in plan, with overall dimensions of 670 m by 910 m (2200 ft by 3000 ft), with an average thickness of 185 m (600 ft). The top of the deposit is at an elevation of 2610 m (8560 ft), while the lower limits range from 2,340 m (7680 ft) on the west to 2,100 m (6900 ft) on the east. The mineralization is relatively continuous in the ore bodies and consists of molybdenite and quartz in random intersecting closely spaced veinlets. The general nature of the orebody and the surrounding host rock is that of very competent (high strength) granite with compressive strengths ranging from 100 to 275 Mpa (14,500 to 40,000 psi). Host rock areas that have very little molybdenite have been found to behave appropriately for medium-strength granite. The proposed UNO facilities will be located under Harrison Mountain, which is situated just to the west of Red mountain (Figure 8). Regional geologic studies have indicated the Harrison Mountain area to be barren of mineral deposits, and for this reason extensive exploration drilling has not been performed. The Henderson Geology Staff_ carried out detailed surface mapping of Harrison Mountain in the early 1980's. This mapping revealed highly competent Precambrian Silver Plume Granite along the crest of the mountain, and on the northeast and southeast-facing slopes. Broad zones, up to 300 m (1000 ft) wide of northeast-trending broken and fractured granite were mapped along the upper northwest slopes below the ridgeline. This broken zone lies within the overall trend of the Vasquez Pass Shear Zone. The downward extent of this broken zone is not known. It does, however, project to the northwest of the proposed UNO excavation, one mile below the peak. The only exploratory drill hole located on Harrison Mountain was CX-126, drilled in 1968 from an elevation of 3502 m (11,489 ft) on the southeastern slope. The hole was drilled from an access road below the saddle that separates Harrison from Red Mountain, and is above the trace of the proposed access tunnels on 7500 Level. The vast majority of the core was in Precambrian Silver Plume Granite, with minor intervals of Idaho Springs Schist that occur as inclusions. What is noteworthy in this hole is that the Silver Plume Granite becomes more competent with depth, beginning at around 2957 m (9,700 ft) in elevation. Rock competencies range between 6 to 8 (with 9 being maximum). The contact between Silver Plume and Urad Porphyry is at an elevation of 2654 m (8706 ft), with rock competencies remaining high to the end of the hole at an elevation of 2294 m (7526 ft). The bottom of this hole is very close to the 9HW-99LD intersection on 7500 Level. This intersection is the preferred location of a 600 m (2,000 ft) exploration drill hole to the west under Harrison Mountain. Diamond drill holes to the north of CX -126 corroborate the high rock competencies seen in that drill hole. Drill holes CX-135 and CX-103 both show high competencies in the Silver Plume Granite and in the Urad Porphyry. Silver Plume Granite has historically been a competent unit during underground development at the Henderson Mine. On the 7500 Level, the Granite remained competent in 9A and 9HW drifts. Based on the detailed geologic logs from surface exploration diamond drill holes and the information gathered by mining through the Precambrian units on the 7500 Level, the proposed large UNO excavation under Harrison Mountain should be in competent Precambrian Silver Plume Granite. Exploratory drill holes from the 7500 Level will be necessary to verify this conclusion.

Two MSHA approved emergency escape routes for the safe evacuation of mine personnel in the event of a mine emergency exist. The primary escape way is Number 2 Shaft, and the secondary escape way is through the PC2 tunnel. The largest excavations in the mine were constructed as part of the Henderson 2000 project. These were the PC1/PC2 transfer station, 12.8 m wide _ 27.5 m long _ 17.7 m high (42 ft _ 90 ft _ 58 ft) constructed in Silver Plume Granite, and the underground crusher station 18.6 m wide _ 28.3 m long _ 14.6 m high (61 ft _ 93 ft _ 48 ft), constructed in the Vasquez Porphyry rock type.Two MSHA approved emergency escape routes for the safe evacuation of mine personnel in the event of a mine emergency exist. The primary escape way is Number 2 Shaft, and the secondary escape way is through the PC2 tunnel.

Mine ventilation: The mine ventilation system has a capacity of 1,900,000 cubic feet per minute (cfm) provided through three large surface fans. Of this total amount, about 200,000 cfm in excess capacity would be available to UNO, which is significantly more than the estimated 50,000 cfm that would be required to ventilate the large UNO room and access tunnels.
Electricity: Two 24 MW transformers for a total of 48 MW are available at the mine site. The mine is currently using 10 MW, but also requires an additional 10 MW for backup. With the existing transformer stations, UNO would have 14 MW available with 14 Megawatt for backup. The electrical network has 100% redundant feed from the power company, Xcel Energy, from the Cabin Creek substation near Georgetown and Blue River substation located between Kremmling and Silverthorne.
Mine dewatering: The mine pumping and dewatering system has a capacity of 5000 gpm. the mine is currently using about 1000 gpm.
Water treatment: The surface water treatment facility has a capacity of 4000 gpm. The mine is currently using about 1100 gpm normally and about 2000 gpm during spring runo_, leaving about 2000 gpm available.
Compressed air: There are two 8000 cfm, one 6000 cfm, and one 1700 cfm compressors available as part of the mine compressed air system. The mine currently uses about 6000 cfm, leaving in excess of 16000 cfm available.
Concrete batch plant: A concrete batch plant for mixing concrete and shotcrete that would be required during construction is available. The batch plant has a capacity of 200 yd3 per day, of which the mine is currently using about 60 yd3 per day. About 140 yd3 per day would be available.
Rock conveyor system: The mine conveyor system for rock removal was designed for a capacity of 40,000 tons per day. The mine is currently using about 21,000 tons per day. The estimated maximum that would be required for mine production is 30,000 tons per day, leaving at least 10,000 tons per day available.
Outreach facilities: An area at the mine site about 4 acres in size is available for the con- struction of outreach facilities.

Summary:
Considering only the primary factors such as geology, cost, quality, environmental impact, the Henderson Mine is a very strong competitor for siting UNO and other underground science experiments. When other important factors such as cooperation from mine ownership, accessibility, proximity to industry, technicians, and major academic institutions, are included, Henderson becomes the preferred choice for UNO. As a potential national facility, when such additional factors as quality of life, educational, recreational, and cultural amenities are also considered, Henderson offers a very attractive package. With a minimum 5,000' overburden at the proposed UNO excavation cavity, the Henderson Mine is deep enough to meet the low cosmic ray background levels required for UNO and most other proposed underground experiments. Deeper levels are readily achievable at relatively low cost. Preliminary estimates suggest that levels at 7,000' can be reached with primary and secondary tunnels in less than a year for around $20M. Preliminary geological studies indicate that the rock at the proposed excavation site is likely to be Silver Plume granite, ideally suited to large cavity excavation. Funding has been secured to verify this by performing a core-drilling. As a recently upgraded modern mine, Henderson is safe and has the infrastructure and excess capacity to accommodate easily the additional excavation and infrastructure support required for the UNO experiment. Its main shaft is large enough (28' diameter) to accommodate sea containers, and it has in place the necessary excess electrical power and water treatment capacity to meet the needs of an underground laboratory. Furthermore, the efficiencies of its high capacity excavation and rock removal methods will save tens of millions of dollars in excavation costs. It is also important to note that the environmental impact is fully accommodated within Henderson's existing permits. When the mine ceases operations (estimated between 15-25 years), the conveyer tunnel will provide a convenient high capacity horizontal access as well. All the major local stake holders are very supportive of this project. Of particular importance is Phelps-Dodge, the parent company of the Climax Molybdenum Henderson Mine. They own not only the mining operations but all the land involved in the project. They have been fully cooperative and supportive, providing access to mine documents such as sites plans, environmental impact reports, radon levels, ventilation capacity etc. Though the legal relationship between the company and a national facility would need to be defined in detail, they have expressed a great willingness to pursue the initiative.
It is remarkable that, as one of the ten largest underground operating mines in the world, the Henderson Mine is located within minutes of an interstate highway and just an hour's drive from a major metropolitan area with its broad supporting base of technical industries, highly trained workforce, research universities, and a major international airport - not to mention four professional sports franchises. It is worth mentioning as well that seven major mountain and ski resorts are located within an hour of the mine.
Henderson Mine provides an historically unique opportunity for the nation to create - at relatively modest cost and in a highly desirable location - the major underground facility needed to address some of the deepest questions of contemporary physics.