Ore Minerals: Finding, Mining, Processing, and Governance

Learning Objectives

  • Describe how ore minerals are found through geological exploration.
  • Identify and distinguish between the different methods of surface and underground mining.
  • Explain the primary steps, technical processes, and equipment involved in mineral processing and milling.

Fundamentals of Ore Minerals and Deposits

  • Rock Seam or Ore: A natural rock or sediment containing one or more valuable minerals. It is defined as a metalliferous mineral, or an aggregate of metalliferous minerals and gangue, that can be extracted and mined at a economic profit.
  • Gangue: The associated rock or mineral material of no economic value that surrounds valuable minerals within an ore deposit.
  • Mineral Ores: Rock deposits containing metallic or non-metallic minerals. Common mineral types include:
    • Metallic ores: Chalcopyrite, bornite, azurite, chrysocolla, malachite, cuprite, native copper, galena, gold, iron, and magnetite.
    • Non-metallic and industrial ores: Gems, sulfides, carbonates, silicates, chrysotile asbestos, aggregate, sand, and soil.
  • Mineral Deposit vs. Ore Deposit Distinction:
    • Mineral Deposit: A natural occurrence of a useful mineral in the Earth's crust; this is strictly a geologic term.
    • Ore Deposit: A mineral deposit of sufficient size, grade, and concentration to invite commercial exploitation and mining; this is an economic term.
  • Geographic Distribution in the Philippines: Mineral deposits are located across various regions, including:
    • Magnetite deposits in the Ilocos Region.
    • Chromite, manganese, and gold deposits distributed across key mineralized provinces.

Mineral Exploration Methods

  • Mineral Exploration: A complete sequence of scientific and technical activities aimed at discovering deposits of minerals and rocks capable of meeting society's resource needs.
  • Stage 1: Project Design
    • The initial planning phase of a mineral discovery project.
    • Involves comprehensive review of existing data (geologic reports, mining histories, topological maps).
    • Identification of statutory government requirements and legal permitting for acquiring exploration rights.
    • Review of social, environmental, political, and economic acceptability of the proposed project.
    • Formulation of budget proposals and project management organizations.
  • Stage 2: Field Exploration
    • Physical on-site scientific investigation divided into three sequential phases:
    • Phase A: Regional Reconnaissance: Broad-scale mapping and sampling over large geographical regions to identify prospective targets or mineralized zones.
    • Phase B: Detailed Exploration: Concentrated surface and subsurface mapping, trenching, and geophysical survey work to delineate target boundaries.
    • Phase C: Prospect Evaluation: Quantitative assessment of commercial feasibility through:
      1. Extensive resource, geotechnical, and engineering core drilling.
      2. Metallurgical testing of core samples.
      3. Environmental and societal cost assessments.
  • Stage 3: Pre-production Feasibility Study
    • Comprehensive technical and economic analysis validating the accuracy of all accumulated exploration data.
    • Submitted to independent assessors and potential investors to raise financial capital required for mine construction.
    • Covers four essential feasibility parameters:
    • Economic Feasibility: Formal cost-benefit analysis and financial modeling.
    • Technical Feasibility: Engineering risk assessment and operational solutions.
    • Operational Feasibility: Analysis of management controls, operating efficiency, and required infrastructure/services.
    • Schedule Feasibility: Timeline projections and resource scheduling.

Methods of Mining

  • Historical Context: Mining traces back to prehistoric times. Flint was the first mineral extracted due to its conchoidal fracturing pattern, which allowed humans to shape sharp-edged tools, scrapers, knives, and arrowheads.
  • Mining Definition: The physical process of mineral extraction from a rock seam or ore body located on the Earth's surface, underground, or underwater.
  • Surface Mining Methods:
    • Utilized when ore bodies are positioned close to the Earth's surface.
    • Surface mining excavator and heavy haul truck
    • Open-Pit Mining: The most common surface extraction method. Involves drilling and blasting rock with explosives to create a massive pit or excavation. Widely used for extracting gravel, sand, building stone, and metal ores.
    • Dredging: Excavation of mineral deposits from beneath water bodies (rivers, lakes, oceans). Deep-sea dredging architectures utilize a Mining Support Vessel (MSV), a Riser & Lifting System (RALS), and a Seafloor Mining Tool (SMT).
    • Strip Mining: Involves stripping away a thin layer of overburden (soil and rock) above an ore seam, depositing overburden behind the cut, excavating the ore, and cutting parallel strips while depositing new spoil onto cleared areas. Used for coal, phosphate, clay, and tar sand deposits.
    • Quarrying: Open-cut mining specialized for extracting dimension stone or construction aggregate.
    • Placer Mining: Mining of alluvial stream bed deposits containing heavy minerals using open cuts, panning, or surface tunneling excavators.
    • Other Surface Techniques:
    • Mountaintop Mining: Clearing mountain ridges using draglines and placing waste rock spoil in adjacent valleys (valley fill).
    • Contour Mining: Excavating ore along steep terrain contours using bulldozers.
    • Highwall or Auger Mining: Using continuous auger drills to extract ore directly from exposed vertical highwalls.
    • Area Mining: Operating draglines systematically across flat terrain.
  • Underground Mining Methods:
    • Utilized when target ore bodies are buried deep within the crust.
    • Primary Entry Configurations:
    • Shaft Mine: Vertical entry shaft equipped with coal elevators and miner's elevators.
    • Drift Mine: Horizontal tunnel driven directly into hillside ore seams.
    • Slope Mine: Inclined access shaft connecting surface facilities to sub-surface levels.
    • Internal Mine Workings & Infrastructure:
    • Head frame, hoisting skips, skip-filling station, ventilation shafts, haulage levels, ramps, underground rock crushers, ore storage bins, sumps, pump stations, water basins, settling ponds, producing stopes, and backfilled mined-out stopes. (Reference: H. Hamrin, Guide to Underground Mining Methods and Applications, Stockholm: Atlas Copco, 1997 / Encyclopædia Britannica, Inc., 2007).

Mineral Processing and Milling

  • Milling or Mineral Processing: The industrial process of extracting valuable minerals from mined ore, refining them, and preparing them for commercial use. It is the art of treating crude ores to separate valuable minerals from waste rock or gangue.
  • Primary Steps in Mineral Processing:
    1. Sampling: Extraction of a small, representative portion of the mined bulk material required for analytical testing.
    2. Analysis: Quantitative evaluation of ore composition, including chemical assaying, mineral identification, and particle size distribution analysis.
    3. Comminution: Mechanical size reduction process that liberates valuable minerals from surrounding gangue through successive crushing and grinding stages.
    4. Concentration: Physical or chemical separation processes that isolate valuable mineral particles from raw waste rock.
    5. Dewatering: Liquid-solid separation using filtration, sedimentation, and drying to convert aqueous slurries into dry concentrate products.
  • Comminution & Circuit Engineering Details:
    • Flowchart of mineral comminution, extraction, and refining
    • Circuit Flow: Run-of-mine ore →\rightarrow Crushing →\rightarrow Screening (oversize recycled to crushing) →\rightarrow Grinding →\rightarrow Classification (oversize recycled to grinding mill).
    • Crushing Equipment: Primary Jaw Crusher handling input sizes <110 mm< 110\,\text{mm}. Secondary Scats Crusher reducing 80 mm80\,\text{mm} feed to 15 mm15\,\text{mm} product size. Stockpiles handle crushed ore volumes up to 20,000 t20,000\,\text{t} at sizes <275 mm< 275\,\text{mm}.
    • Grinding Equipment: Semi-Autogenous Grinding (SAG) Mill (2,100 kW2,100\,\text{kW}, 4.8 m×5.7 m4.8\,\text{m} \times 5.7\,\text{m}) and Ball Mill (1,100 kW1,100\,\text{kW}, 3.6 m×6.0 m3.6\,\text{m} \times 6.0\,\text{m}).
    • Classification Equipment: Primary Hydrocyclones (26′′/90 kPa26''/90\,\text{kPa}) and Secondary Hydrocyclones (10′′/120 kPa10''/120\,\text{kPa}).
    • Leaching & Carbon Adsorption: Process slurries pass through 5×5 \times Leach Tanks (700 m3700\,\text{m}^3 capacity each) with lime and oxygen dosing, followed by 6×6 \times Adsorption Tanks (350 m3350\,\text{m}^3 capacity each).
    • Product Recovery: Loaded carbon carrying 1,000 ppm Au1,000\,\text{ppm Au} and 6,000 ppm Ag6,000\,\text{ppm Ag} moves to elution. Smelting and refining deliver market-ready metal slabs at 99.99%99.99\% purity. Gangue waste and tailings are dispatched to tailing ponds, tailing disposal sites, or mine void fills.
  • Specific Separation & Extraction Methods:
    • Heavy Media Separation: Denser minerals sink while lighter minerals float when immersed in heavy liquid media.
    • Magnetic Separation: High-intensity magnetic fields extract magnetic minerals from non-magnetic gangue.
    • Flotation (Froth Flotation):
    • Diagram of Froth Flotation system
    • Powdered ore is mixed with water and flotation reagents/oils to make a pulp slurry. Air is introduced and stirred by a rotating paddle. Hydrophobic valuable minerals attach to rising air bubbles, accumulating as a top mineral froth that is skimmed off, while hydrophilic gangue remains in the liquid.
    • Cyanide Heap Leaching: Applied to low-grade gold ores; crushed ore is stacked on lined pads and irrigated with a sodium cyanide solution to dissolve target gold particles.

Environmental, Socio-Political, and Governance Considerations

  • Philosophical Framework: Environmentalist Gina Lopez stated that mining is a conditional privilege rather than an inherent right, whereas citizen access to clean water, air, and healthy ecosystems is a constitutional and fundamental right that governments are obligated to protect.
  • Socio-Political Reality: Recent developments include the approval of nickel mining projects despite inadequate local consultation and grave health and environmental risks to resident communities (e.g., Amnesty International report, January 2025).
  • Civic Action via Formal Petitions: Petitions addressed to regulatory authorities such as the Department of Environment and Natural Resources (DENR) serve as formal instruments to advocate for responsible mining, community safety, and environmental protection. Required petition elements include:
    1. Proper Greeting
    2. Brief Introduction
    3. Concise Statement of Concerns
    4. Polite Appeal or Specific Requests
    5. Closing Statement
    6. Signatures

Discussion and Application Questions

  • 1. What mineral deposits are present in sub-surface rock layers?
  • 2. Given that sub-surface structures are hidden, what methods and techniques can be suggested to discover hidden mineral deposits?
  • 3. What steps and processing methods are used to separate individual mineral components from raw mined ore?