24-MMP-A1 General Geology and Exploration · December 2018
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, 2018-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: Klein & Dutrow, Manual of Mineral Science, 23rd ed. (crystal systems, diagnostic physical properties, hand-specimen identification); Guilbert & Park, The Geology of Ore Deposits (genetic classification, deposit-type descriptions throughout); Evans, Ore Geology and Industrial Minerals, 3rd ed. (deposit classification, structural controls on ore); Telford, Geldart & Sheriff, Applied Geophysics, 2nd ed. (gravity, magnetic, electrical, EM and seismic methods); Rose, Hawkes & Webb, Geochemistry in Mineral Exploration, 2nd ed. (sample-medium selection, dispersion patterns); Peters, Exploration and Mining Geology, 2nd ed. (drilling methods and sampling).
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.
Given. Reading the cross-section by cross-cutting relationships and superposition: the folded package is (bottom/oldest to top/youngest) Gneiss → Schist → Slate, intruded by Granite (cutting the folded units, so younger than them); this whole assemblage is bevelled flat by erosion (the angular unconformity) and then buried under a flat-lying cover, oldest to youngest, of Volcanic Breccia & Tuff → Fossiliferous Chert → Limestone → Sandstone; a normal fault (down-to-the-right) then cuts the basement, the unconformity AND the cover; and finally a basalt dike intrudes along the same steep trend, cutting everything present – including the youngest cover unit, Sandstone – and is truncated only at today's ground surface, making it the youngest event of all. Quartzite, Shale and Pegmatite are printed in the legend but do not appear anywhere in the actual drawing (the same trick already flagged for Pegmatite by the exam itself).
Find. The best answer, with reasons, for each of the five multiple-choice items (i)–(v).
| Item | Answer | Reasoning |
|---|---|---|
| (i) oldest→youngest rocks | [E] none of the above | [A] and [B] are the only options built from rocks that plausibly exist in the section, but both have an inverted pair: [A] places slate BEFORE schist, when schist (higher metamorphic grade, deeper in the un-overturned fold) is actually older than slate; [B] places chert BEFORE granite, when the granite intrudes the folded basement and so must predate the chert, which is part of the cover deposited only after the unconformity. [C] and [D] both name pegmatite, a legend entry that is not present in the drawing at all – and [A] relies on quartzite, which is equally absent. No option survives. |
| (ii) oldest→youngest events | [E] none of the above | [A] opens with "deposition of sandstone" – sandstone is the YOUNGEST cover unit, not the oldest event. [B] places metamorphism last, when it is one of the OLDEST events (it predates the unconformity by a wide margin). [C] places faulting before granitic intrusion, but the fault is shown cutting the granite, so intrusion must come first. [D] invokes "metamorphism of limestone" – the limestone in this section is flat-lying, undeformed cover; it was never metamorphosed. |
| (iii) oldest→youngest events | [E] none of the above | [A] opens with faulting (one of the youngest events) and again invokes pegmatite. [B] places dyke (dike) intrusion BEFORE volcanism, but the dike cuts through the Volcanic Breccia & Tuff cover unit, so that volcanism must be older than the dike, not younger. [C] places faulting BEFORE erosion, but the fault clearly cuts the already-eroded unconformity surface and the cover deposited on it, so erosion is older than the faulting. [D] repeats the fabricated "metamorphism of limestone." |
| (iv) earliest→latest environments | [A] burial in the lower crust, surface exposure, deep ocean | The three environments recorded, in order, are: deep burial and high-grade metamorphism forming the gneiss/schist/slate package (lower crust); uplift and erosion cutting the angular unconformity (surface exposure); then marine/volcanic deposition of the cover sequence (an oceanic environment). [B] and [C] both put "burial" LAST, which is impossible – deep burial/metamorphism must come before a rock can later be exhumed to the surface. [D] puts surface exposure BEFORE burial, also backwards. |
| (v) "there has been..." | [C] deformation without metamorphism | The section records TWO distinct deformation episodes: the early ductile folding of the Gneiss–Schist–Slate package, which WAS accompanied by metamorphism (that is what made them metamorphic rocks in the first place); and the later, purely brittle faulting that offsets the unmetamorphosed cover (Sandstone, Limestone, Chert, Volcanic Breccia & Tuff) without converting any of those units to metamorphic rock. That second, younger episode is exactly "deformation without metamorphism." [A] is not supported – the offset shown is a simple down-to-the-right translation with no evidence of block rotation (bedding dip is unchanged across the fault). [D] is false: the granite and the basalt dike are separated by an entire erosion-and-cover-deposition episode, so they are not synchronous. |
A joint is a naturally occurring fracture in rock across which there has been no significant displacement parallel to the fracture surface – this is the property that formally distinguishes a joint from a fault, where measurable displacement HAS occurred (the small tick mark on the far left of Fig. 3a, cutting only the Sandstone and Limestone with no offset of the layers across it, is drawn as an example of exactly this kind of feature). A joint set is a group of joints that share a common, systematic orientation, produced by the same regional stress episode; two or more intersecting joint sets divide a rock mass into a regular network of blocks.
Joints are extremely relevant to mining engineering for two largely independent reasons. First, GEOTECHNICALLY, joints are pre-existing planes of weakness that control the strength, deformability and failure mode of a rock mass far more than the intact rock strength does – the stability of an open-pit slope, an underground stope back, or a tunnel crown is governed primarily by the orientation, spacing, persistence, roughness and infilling of the joint sets present, and kinematic failure modes (planar sliding, wedge failure, toppling) are analyzed directly from joint-set orientation data (e.g. on a stereonet) relative to an excavation's geometry. Second, ECONOMICALLY/GEOLOGICALLY, joints are the principal permeability pathways along which hydrothermal ore-forming fluids migrate through otherwise low-permeability rock: open joints and joint intersections focus fluid flow, and ore minerals commonly precipitate directly as fissure-fill veins within them, while densely jointed rock ("stockwork") can host large-tonnage, low-grade disseminated mineralization distributed through thousands of individual joint-controlled veinlets, as in porphyry copper deposits.
