Phosphate Mineral Resource/Reserves and Prefeasibility Study

Agapito Associates, Inc. (AAI) was commissioned by Stonegate Agricom Ltd. to complete a Canadian National Instrument 43-101 independent Mineral Resource/Mineral Reserve estimate and Preliminary Feasibility Study (PFS) for the Paris Hills Phosphate Project located in Paris, Idaho.  The Project represents a new underground phosphate rock mine in southeast Idaho and the first new underground phosphate mine to operate in the Phosphoria Formation since the 1970s. 

AAI initially participated in the design of the exploration drilling program, geological logging program, and quality assurance/quality control (QA/QC) protocol for assaying.  Carlson Software was utilized to develop a computer geologic block model of the bedded deposit for estimating the Mineral Resource.  Block values were estimated utilizing an unbiased geostatistical (kriging) estimator.

The PFS encompassed the exploration, geologic modeling, resource and reserve estimation, mine planning and design, mining methodology and equipment, hydrogeology modeling, surface infrastructure requirements, labor, beneficiation test work results, fertilizer processing pilot plant test work results, phosphate rock ore handling, environmental and permitting, mine closure, marketing, royalty agreements, project economics, project development schedule, and risks in support of a direct shipping run-of-mine ore (phosphate rock concentrate) greater than 29 percent phosphorus pentoxide (P₂O₅). 

A detailed underground room-and-pillar mine plan with partial pillar extraction was developed at mining depths ranging from outcrop to more than 600 meters (2,000 feet) deep.  Mine projections were developed based on key deposit parameters, geotechnical analysis, and equipment constraints, which included thin seam and steeply dipping mining conditions, a soft rock environment, high groundwater inflows, and the need to minimize out-of-seam dilution to achieve a direct-ship phosphate rock concentrate.  The PFS considered key transportation alternatives for delivering phosphate concentrate to market, including an option to truck the ore to a Montpelier, Idaho, rail loadout facility located on the Union Pacific Railroad.

AAI coordinated subconsultant experts on marketing (CRU International Ltd), hydrology (Whetstone Associates, Inc.), seismic interpretation (Boyd PetroSearch), traffic studies (J-U-B Engineers, Inc.), environmental (Brown & Caldwell), and various components of surface site facilities and infrastructure design (DcR Engineering).  AAI completed the geotechnical design which included laboratory rock mechanics testing of core from the exploration program. 

The PFS identified the project as having a $242 million pre-tax net present value (NPV) (8% annual discount rate) with a 4.6 year pre-tax payback, and an after-tax NPV of $179 million. 

AAI authored two NI 43-101 Technical Reports, one at the Mineral Resource stage and the second following completion of the PFS and Mineral Reserves declaration.  AAI engineers and geologists served as Qualified Persons for the Technical Reports.

14th United States/North American Mine Ventilation Symposium, University of Utah, Salt Lake City, Utah, June 17, 2012

Authors: S. B. Patton and G. L. Skaggs (Agapito Associates, Inc.) and S. Britton (Baja Mining Corporation)

Boleo is an underground copper-cobalt-zinc-manganese project currently under construction near the town of Santa Rosalía in the state of Baja California Sur, Mexico.  The deposit consists of seven soft-rock ore beds, or “mantos”, faulted into irregular-sized blocks of mineable ore.  Over 94 percent of ore will be derived from underground mining.  Current plans show over thirty underground mines will be developed during the anticipated project life in Mantos 1, 2, 3 and 4.  Underground mining operations will consist of room-and-pillar mining with pillar recovery using standard drum-style continuous mining machines, shuttle cars, and continuous haulage typically found in coal, potash and salt mines.  Upon achieving steady-state full production, the Boleo underground mines will have up to six continuous mining units set up at one time, either mining on advance or retreat, with no more than three units in any one mine at the same time.  The challenge to the ventilation design is to size and design the controls for a main mine fan that would be interchangeable between mines operating at various production rates and operating lives.  To manage risks to workers associated with heat stress and strain during the hotter months of operation, mine ventilation air cooling is also necessary.  This paper presents the ventilation design, fan and cooling system selection for the Boleo mines.

Downloadable PDF:  Ventilation Design for the Boleo Project

Elk Creek Geotechnical Program

Agapito Associates, Inc. (AAI) has been involved in long-term geotechnical investigation and design at the Oxbow Mining, LLC, Elk Creek Mine, dating back to the pre-development phase.  Services provided by AAI include horizontal stress measurement, numerical modeling of seam interaction, rock mechanics testing, and mine-wide roof and floor characterization.  Future mining involves increased cover depth, and one of the primary areas of work is in developing pillar design strategies appropriate for the increased cover.  Recently, AAI designed and installed an extensive geotechnical instrumentation system for characterizing ground response to longwall abutment loading, including pillar loading, entry convergence, and roof deflection.  The resulting data was used to calibrate numerical modeling inputs to observed ground response.  Modeling and other design approaches were then used to develop a range of pillar design strategies for Oxbow in support of mine planning.

Weeminuche Construction Authority

After detailed design of cable trenches and final instrument specifications included as part of the instrument procurement process, AAI mobilized a field crew to the Ridges Basin Dam sight in June of 2005 to drill the boreholes and install the first piezometers and the inclinometer into the foundation rock at the bottom of the dam excavation.  Over the next 2 years, AAI installed 27 fiber-optic piezometer transducers and 21 vibrating-wire piezometer transducers plus 3 vibrating-wire weir gage level transducers.  An inclinometer casing and 4 survey instrument piers were also installed at the dam.  Over 48,000 feet of fiber-optic and vibrating-wire cable was installed in trenches and pulled through the conduit into the Control House where AAI installed the data acquisition hardware.  Instrumentation and data acquisition hardware installation was completed in September of 2007.

SD-1500 at Ridges Basin Dam

Occidental Oil Shale

This project involved a proposed in-situ retort oil shale mine located in Piceance Creek Basin, Rio Blanco County, Colorado.  The scope of work included:  (1) prepare a mine layout and operations plan, (2) evaluate the existing facilities and develop plans and estimates for modifications to support the new mining plan, (3) develop design engineering, cost estimate and schedule of new 1800-ft-deep off-gas (high temperature gas) shaft, (4) review condition of existing shafts, shaft liners, and hoisting equipment and facili-ties, (5) design new mine and MIS support facilities, and (6) prepare a capital and operating cost estimate for mining and retort development.

The mine layout was developed to utilize the existing shafts and shaft stations, minimize development costs while main-taining essential safety functions.  Seventeen retorts and room-and-pillar areas were considered for supplementary oil shale production.  The modified in-situ process required a dedicated off-gas exhaust shaft involving selection of construction methods, design, and a cost estimate.

Of the existing facilities, shaft liners needed some upgrade, stations required remedial attention, water handling in the shafts required installation of new control measures, and hoisting systems needed some refurbishment.  Loading pocket facilities required completion, provision made for shaft bottom clean-out, and the headframe loadout modified.

The design of the new mine and MIS support facilities incorporated mining sequencing, ground support, mining equipment selection, materials handling, ventilation, and underground services.  The capital cost estimate, prepared from design drawings, included a detailed scope of work and engineering estimate for Year 1 of the project.  An operating cost estimate for the mine was also prepared following similar procedures.  A spreadsheet-based cost model was used to facilitate mining cost calculations.

Confidential Energy Client 

Agapito Associates, Inc. (AAI) completed a geotechnical evaluation of cavity stability, inter-cavity pillar sizing, and subsidence potential for a proprietary, concept-level borehole hydraulic mining method developed for extracting bitumen-rich oil sands in the Athabasca oil sand deposit in northern Alberta, Canada. 

Numerical modeling was conducted using FLAC to simulate cavity response during the mining sequence.  The model simulated the complex non-linear and pore-pressure dependent behavior of the oil sands.  Under low cavity pressures, cavity stability was shown to be controlled by mechanical degradation of the oil sands caused by gas exsolution. 

Surface and subsurface subsidence caused by pillar convergence and overburden movement was modeled over a wide range of mining depths.  Alternative mining geometries and the use of backfill were evaluated for optimizing the mining process, minimizing subsidence, and maximizing resource extraction.

Underground Coal Gasification Cavern Subsidence

GasTech, Inc. (GasTech) is in the process of permitting a series of underground coal gasification (UCG) wells as part of a pilot project in the deep coals of the Powder River Basin (PRB), Wyoming.  GasTech commissioned Agapito Associates, Inc. (AAI) to analyze the long-term behavior of UCG caverns after completion of the pilot project.  The analysis provided estimates of surface and aquifer displacements, and stability assessments of the pillar between rows of caverns.

Numerical analysis was performed to account for extraction-induced stress changes and the non-elastic behavior of the weaker coal seams.  Five types of input were considered in the analysis: cavern geometry, stratigraphy, rock properties, in-situ stress, and groundwater pressure.  The main coal-producing seams were represented in the model, including the target Upper Wyodak coal bed which is about 60 feet thick at a depth of about 1,000 feet below ground.  In-situ stresses were based on nearby hydrofracture measurements.  Modeling was performed using FLAC3D.

Geotechnical issues addressed include estimated height of roof collapse above the UCG caverns, estimated disturbance of aquifers, and the potential for surface subsidence.  Recommendations were developed for well spacing to optimize resource recovery given limitations on subsidence.

Chevron Mining, Inc.

Highwall Slope Stability

AAI has investigated various aspects of highwall stability at several pits at the Kemmerer Mine, including large-scale slope failure, wedge analysis, and most recently, rockfall risk assessment. Alternative catch bench and berm designs were evaluated using the statistical CRSP program and numerical UDEC models. Both programs were calibrated using on-site experimental measurements.

Highwall Mining Evaluation

A comprehensive evaluation was completed of the geotechnical and operational issues related to conducting highwall mining in three different pits. The combination of multiple thick, steeply dipping seams and variable topography resulted in a challenging optimization study balancing recovery, practicality (cost), and safety. Candidate mining configurations involved varying the opening inclination and mining height (multiple passes) and using multiple lifts. Several empirical design techniques were employed in addition to a number of numerical models to develop pillar design charts for the optimum opening configuration. The weakening effect of the highwall mining openings on overall slope stability was also analyzed.

Uranium Resource Estimate 43-101

Agapito Associates, Inc. (AAI) was engaged by Concentric Energy Corporation to complete the original independent NI 43-101 Technical Report and resource estimate for the Anderson Mine uranium and vanadium property located near the town of Wickenburg, Yavapai County, in west-central Arizona, USA. Mineralization occurs in the sequence of Miocene-age lacustrine (lake-bed) sediments which unconformably overlie andesitic volcanics. The uranium-vanadium resource was defined by 1,393 vertical exploration drill holes, including 1,320 downhole gamma surveys and a total of 5,596 chemical assays, completed by Minerals Exploration Company of Union 76 Minerals, a subsidiary of Unocal Corporation, and Urangesellschaft U.S.A., Inc. in the 1970s.

AAI coded a Visual Basic program based on the classic U.S. Atomic Energy Commission GAMLOG algorithm to convert natural gamma radiation counts taken from historical logs to equivalent radiometric grades of uranium oxide (U3O8), with adjustments for hole characteristics and disequilibrium. Composite grades and thickness were determined for multiple radiometric beds in each drill hole and applied to a computer block model to estimate the grade and quantity of mineralization. Historical measurements were validated by confirmation drilling overseen by AAI’s NI 43-101 Qualified Persons in 2006.

The 43-101 Technical Report was submitted for the first time to the Toronto Stock Exchange in 2010 following Global Uranium Corporation’s acquisition of the project.