Ore Study Guide

📖 Core Concepts Ore – Natural rock/sediment containing valuable minerals in concentrations high enough for economic extraction. Ore Grade – Concentration of the target material, expressed as % or g t⁻¹ (grams per tonne). Economic Viability – An ore is viable when the value of extracted metals > costs of mining, processing, and environmental compliance. Gangue – Non‑valuable material that must be separated from the ore. Liberation – Breaking the rock so that mineral grains are freed from gangue. Concentration – Physical/chemical processes that isolate liberated minerals (e.g., flotation, gravity). Tailings – Waste left after mineral extraction; may contain toxic or radioactive elements. Ore Deposit vs. Mineral Resource – A deposit is the economically extractable subset of a resource, which includes all known material regardless of profit‑ability. 📌 Must Remember Viability equation: Revenue > Mining + Processing + Environmental costs. Typical porphyry copper grade: 0.8 % Cu (by weight). Key ore‑type minerals: Cu → chalcopyrite, bornite, malachite Fe → hematite, magnetite, siderite Au → native gold, electrum Ni → pentlandite, garnierite REE → bastnäsite, monazite, xenotime Major deposit families: Magmatic (e.g., pegmatite, carbonatite), Metamorphic (skarn, greisen), Hydrothermal (MVT, VMS, orogenic gold), Sedimentary/Marine (laterite, BIF, placer). Environmental red flags: Acid‑generating sulfides → sulfuric acid formation → low pH in soils/waters. Toxic elements (Hg, As, Pb, Cr, U) → health hazards. 🔄 Key Processes Prospecting – Remote sensing, geophysical surveys, geochemical sampling → locate anomalies. Exploration – Detailed mapping, diamond drilling → define grade, tonnage, continuity. Feasibility Study – Economic modeling (price, cost, market), engineering design, environmental impact assessment. Development – Build mine, processing plant, infrastructure. Production – Surface: open‑pit, strip mining Underground: block caving, cut‑and‑fill, stoping Followed by liberation → concentration → tailings management. Reclamation – Land reshaping, revegetation, water treatment to restore post‑mining use. 🔍 Key Comparisons Ore Deposit vs. Mineral Resource Deposit: economically extractable, meets viability criteria. Resource: total known material, includes sub‑economic portions. Magmatic Sulfide (Ni‑Cu) vs. Magmatic Sulfide (PGE) Ni‑Cu: formed in komatiites, anorthosites; primary metals Ni & Cu. PGE: hosted in large mafic/tholeiitic intrusions; primary metals Pt, Pd. Porphyry Cu vs. Skarn Cu Porphyry: disseminated, large volume, low‑grade (0.8 % Cu). Skarn: contact‑metamorphic, higher grade, enriched Ca‑Fe‑Mg silicates. Laterite vs. Banded Iron Formation (BIF) Laterite: supergene weathering of mafic rocks → Fe, Mn, Ni, Co oxides. BIF: Precambrian chemical sedimentary layers of alternating chert/Fe‑rich strata. ⚠️ Common Misunderstandings “All high‑grade ores are profitable.” – Ignoring extraction and processing costs can make a high‑grade ore uneconomic. “Gangue is waste and can be ignored.” – Proper gangue removal is essential; leftover gangue can dilute concentrate and raise processing costs. “All sulfide ores generate acid.” – Only acid‑generating sulfides (e.g., pyrite) pose AMD risk; some sulfides are neutral. “Tailings are inert.” – Tailings often retain heavy metals, toxins, or radioactivity; they require careful storage and monitoring. 🧠 Mental Models / Intuition “Ore‑Grade × Deposit‑Size = Potential Value.” Visualize a rectangle: length = tonnage, height = grade; area = total metal. “Liberate before concentrate.” If minerals stay locked in gangue, any concentration step is wasted – think of sorting mixed nuts: you must first crack the shell (liberation) before picking the peanuts (concentration). “Deposit type predicts processing.” Magmatic sulfides → flotation; laterites → hydrometallurgy; placers → gravity concentration. 🚩 Exceptions & Edge Cases Low‑grade but high‑tonnage deposits (e.g., some porphyries) can be viable if processing costs are low and metal prices are high. Acid‑neutralizing gangue (e.g., carbonate‑rich host rock) can mitigate AMD from sulfide ores. Hybrid deposits (e.g., magmatic‑hydrothermal) may require combined processing routes (flotation + leaching). 📍 When to Use Which | Situation | Preferred Method / Tool | |-----------|--------------------------| | Free‑milling, dense minerals (gold, PGEs) | Gravity concentration, heavy‑media separation | | Fine sulfide particles | Froth flotation | | Oxide ores (e.g., laterite nickel) | Hydrometallurgical leaching (acid or ammonia) | | Complex mixed‑mineral ores | Sequential flotation (multiple stages) or combined magnetic/electric separation | | High‑acid‑generating potential | Pre‑oxidation or neutralization before exposure to air/water | | Small, scattered placer deposits | Simple sluicing or dredging | 👀 Patterns to Recognize Geologic setting → deposit type: Convergent margin → porphyry Cu. Mantle plume → kimberlite (diamonds). Tropical weathering → laterite Ni/Co. Mineral assemblage clues: Presence of spodumene → carbonatite REE deposit. Chromite + ultramafic host → podiform chromitite. Environmental flags in reports: mention of pyrite, sulfide oxidation, or heavy‑metal tailings → anticipate AMD mitigation. 🗂️ Exam Traps “All sulfide ores are acidic.” – Only those that oxidize to produce sulfuric acid (e.g., pyrite) cause AMD. “Higher grade always means higher profit.” – Overlook mining/processing cost, market price, and environmental compliance. “Pegmatites only contain industrial minerals.” – Some pegmatites host rare‑earth minerals (e.g., spodumene for Li). “All laterites are iron ore.” – Laterites can be sources of Ni, Co, Mn, or Al, not just Fe. “Tailings are always stored on‑site.” – Some operations use off‑site disposal or re‑process tailings for additional metal recovery. --- Use this guide to review core definitions, memorize high‑yield facts, and spot the patterns that will let you eliminate distractors on the exam. Good luck!