24-MMP-A1 General Geology and Exploration · May 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-May. 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, concordant/stratiform vs stratabound terminology); 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 seismic 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 dispersion, survey design parameters); 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.
A concordant ore body is one whose contacts are parallel to, and conformable with, the bedding/layering of the enclosing sedimentary sequence. Several distinct genetic families produce concordant bodies within sedimentary rocks:
Sedimentary exhalative (SEDEX) Pb-Zn-Ag deposits form as syngenetic to early-diagenetic sulphide layers exhaled onto, or precipitated just below, the seafloor in a rifted, fault-bounded sedimentary basin, interbedded with fine clastic sediment (shale, siltstone); they are among the most laterally continuous, sheet-like concordant ore bodies known. Example: the Sullivan Mine, Kimberley, British Columbia.
Banded iron formation (BIF) is a chemical sedimentary rock – alternating chert and iron-oxide (magnetite/hematite) laminae precipitated directly from Precambrian seawater – and the iron ore itself is simply a discrete, mappable stratigraphic unit within the sequence, hence concordant by definition. Example: the Sokoman Formation iron ores of the Labrador Trough, Quebec/Newfoundland-Labrador.
Mississippi Valley-type (MVT) Pb-Zn deposits, though genetically diagenetic-hydrothermal (Question 2(vii)) rather than purely sedimentary, are confined within, and largely conformable to, a specific carbonate stratigraphic unit, producing concordant to broadly concordant orebodies (with locally discordant karst/breccia-hosted zones). Example: Pine Point, Northwest Territories.
Placer (paleoplacer) conglomerate-hosted deposits form when heavy, resistant ore minerals (gold, uraninite) are mechanically concentrated in a basal conglomerate during deposition; the ore-bearing conglomerate bed is itself a conformable stratigraphic unit. Example: the Witwatersrand gold-uraninite conglomerates, South Africa.
Evaporite deposits (potash, salt) precipitate as concordant beds directly from an evaporating brine within a restricted basin, interbedded with other evaporite minerals and fine clastics in a cyclic sequence. Example: the Prairie Evaporite Formation potash beds, Saskatchewan.
A stratiform deposit is a true, continuous, sheet-like ore layer that is itself conformable and essentially parallel throughout to the bedding of the host sequence – the ore constitutes a genuine, mappable stratigraphic unit in its own right, with a simple tabular internal geometry. A stratabound deposit is confined WITHIN a particular stratigraphic unit or restricted stratigraphic interval, but its own internal geometry need not be a simple parallel sheet – it can be irregular, crosscutting, vein-like or breccia-hosted at the scale of individual ore lenses, so long as the whole deposit does not step outside the bounding stratigraphic package. Every stratiform deposit is therefore stratabound (it satisfies the weaker condition), but not every stratabound deposit is stratiform.
The banded iron formation example above is stratiform: the ore itself is a specific, continuous, bedded iron-formation layer that parallels the enclosing stratigraphy at essentially every scale. Pine Point is the illustrative contrast: it is stratabound (confined to a specific unit of the Devonian Presqu'ile barrier-reef/platform carbonate sequence, never occurring above or below it regionally) but not stratiform, because individually the orebodies are irregular karst-collapse breccia pipes and fracture/vug-fillings that crosscut bedding within that unit rather than forming a single continuous conformable sheet.
This distinction is worth carrying into exploration practice: a geologist mapping a stratiform target can lean heavily on stratigraphic correlation and drill-hole cross-sections projected confidently along strike and dip, because the layer itself is the target. A stratabound-but-discordant target such as Pine Point instead demands mapping the internal control – here, the paleokarst plumbing system within the host carbonate – since knowing only that "the ore is somewhere in this formation" leaves the actual orebody locations undetermined without that additional structural understanding.
