24-MMP-A1 General Geology and Exploration · December 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Mining and Mineral Processing Engineering, 09-Mmp-A1 General Geology and Exploration, 2015-Dec. Closed book; only a Casio or Sharp approved calculator permitted. Questions 1–4 are compulsory; a candidate then completes ONE more question chosen from Questions 5, 6 or 7.
Reference texts: Guilbert & Park, The Geology of Ore Deposits (genetic classification, deposit-type descriptions throughout); Evans, Ore Geology and Industrial Minerals, 3rd ed. (deposit classification, ore-body morphology); Klein & Dutrow, Manual of Mineral Science, 23rd ed. (crystal systems, diagnostic physical properties, hand-specimen identification); Telford, Geldart & Sheriff, Applied Geophysics, 2nd ed. (gravity, magnetic, electrical, EM and radiometric methods); Kearey, Brooks & Hill, An Introduction to Geophysical Exploration, 3rd ed. (survey design and method selection); Rose, Hawkes & Webb, Geochemistry in Mineral Exploration, 2nd ed. (stream-sediment/soil survey design); Peters, Exploration and Mining Geology, 2nd ed. (sampling methods, drilling programs).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
These four terms describe two independent properties of an ore body – its timing relative to the host rock, and its geometric relationship to the host rock's structure – and any combination of one timing term with one geometric term is possible.
| Term | Definition |
|---|---|
| (i) Syngenetic | The ore formed at essentially the same time as, and by the same process as, its host rock (e.g. precipitated together with the enclosing sediment, or crystallized together with the enclosing igneous rock). |
| (ii) Epigenetic | The ore formed significantly LATER than its host rock, introduced by a separate, subsequent process (typically a hydrothermal fluid, weathering front or later intrusion) into a rock that already existed. |
| (iii) Concordant | The ore body's contacts are parallel to, and conformable with, the bedding, foliation or other primary layering of the host rock – a purely geometric description, independent of timing. |
| (iv) Discordant | The ore body's contacts cut across the bedding, foliation or structural grain of the host rock at an angle, rather than following it. |
| # | Deposit type | Classification | Reasoning |
|---|---|---|---|
| 1 | Kiruna-type (magnetite-apatite) | Syngenetic & concordant | Forms by direct magmatic crystallization/accumulation within a volcanic pile, producing lens/sheet-like ore conformable with the host volcanic stratigraphy. |
| 2 | Placer | Syngenetic & concordant | Heavy minerals are concentrated and deposited together with the enclosing gravel/sand at the time that sediment layer accumulates. |
| 3 | Iron oxide-copper-gold (IOCG) | Epigenetic & discordant | Hydrothermal breccia-hosted mineralization introduced after host-rock formation, crosscutting host structure along breccia zones and faults (e.g. Olympic Dam-style). |
| 4 | Pegmatite | Epigenetic & discordant | A dike intruded into pre-existing country rock from residual granitic melt, crosscutting the host's structural grain. |
| 5 | Porphyry | Epigenetic & discordant | Stockwork veinlets introduced by a later hydrothermal fluid, crosscutting the earlier intrusive/country rock irrespective of its fabric. |
| 6 | Sedex | Syngenetic & concordant | Sulphides exhale onto, or precipitate just below, the contemporaneous seafloor, forming sheet-like layers interbedded with (conformable to) the enclosing sediment. |
| 7 | Mississippi Valley type (MVT) | Epigenetic & concordant | The classic mismatched pair: ore-forming basinal brines migrate through the carbonate host long AFTER it was deposited (epigenetic), yet the ore stays confined within, and broadly parallel to, the host carbonate unit (concordant). |
| 8 | Kimberlite | Epigenetic & discordant | A pipe/diatreme intrusion that crosscuts all pre-existing country rock it passes through, emplaced long after the host rock formed. |
| 9 | Banded iron formation (BIF) | Syngenetic & concordant | A chemical sedimentary rock precipitated directly from contemporaneous seawater; the iron-rich laminae are themselves the bedding. |
| 10 | Skarn | Epigenetic & discordant | Metasomatic replacement at an igneous-carbonate contact, introduced well after both the intrusion and the carbonate host existed, with irregular replacement fronts that crosscut bedding. |
| 11 | Laterite | Epigenetic & discordant | A residual weathering profile developed long after the parent rock formed, with its blanket geometry controlled by the modern land surface/water table rather than by the parent rock's original bedding or structure, so it cuts across that structure. |
| 12 | Volcanogenic massive sulphide (VMS) | Syngenetic & concordant | Exhalative sulphides precipitate on the contemporaneous seafloor within an active volcanic pile, forming a lens conformable with the enclosing volcanic/sedimentary stratigraphy. |
