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In Support of the Syngenetic Model for Lode Gold Deposits

By: , Posted on: March 13, 2017

the metallogeny of lode gold deposits

The Metallogeny of Lode Gold Deposit: A Syngenetic Perspective presents evidence to support the syngenetic concept for lode gold deposition. Much of the data are from older papers for the simple reason that we describe the deposits as geologists who worked on them. Modern geological concepts often ignore these older data which is evident in a recent review of the book in the Journal of Economic Geology (vol. 111, no. 6, pp. 1520-1521).

Figure 1: Upper Ec division of Bouma turbidite (GC for gold-bearing veins) showing quartz vein with complex internal structure, overlain by 30-cm-thick turbidite with graded bedding. Massive base of next overlying turbidite (T3A) is at top of photo. Individual units are numbered from base upward. Outcrop location: NAD 83. UTM 20T, 0543478/496511 (Copyright Ulrich Kretschmar)

In Nova Scotia, the fact that the Bouma sequences of the Meguma contain quartz mineralization as bedding parallel layers was well established prior to 1912. Similarly, in the greenstone belts the most economic lode gold deposits occur in proximity to the hiatus at the end of mafic volcanism. Both are interpreted as gold cycles. Bedding parallelism is the rule, not the exception, and the favourable stratigraphy may be identified by accessory sulphides and iron carbonate.  Many porphyries, long considered to be intrusive, can be shown to be crystal tuffs, when properly mapped. The Pearl Lake and Preston East Dome porphyries in the Timmins Camp are prime examples.

Figure 2: Polished slab of quartz unit (QU) or quartz vein, the “Rosetta Vein.” Beaver Dam gold deposit, Cambro-Ordovician Meguma turbidite sequence, Nova Scotia. Illustrated is the sedimentary nature of deposition. Distinct pulses of hydrothermal quartz and sulfide (gold) were deposited with ongoing pelagicepelitic sedimentation during a hiatus in turbidite deposition (same as Figure 2.3). (Copyright Ulrich Kretschmar)

Recent studies on ocean floor vents illustrate that the temperatures and pressures are the same as recorded in quartz-rich lode gold horizons. This correlation suggests that they share the same source. In addition, many of these bands are associated with graphite; this association indicates that these deposits formed in the presence of organic matter. The distribution of amorphous carbon/graphite in the broader geological environment strongly supports deposition on the ocean floor.

Figure 3: A 4-cm pyrite crystal in fine-grained quartz arenites, showing later slaty cleavage being deflected around it (highway road cut, Ecum Secum) (Copyright Derek McBride)

Looking at the subsequent history, one sees that the typical lode gold deposit is moderately to steeply dipping, meaning that the host rocks have been rotated into that position during deformation.  Prior to the primary deformation, these rocks were unconsolidated muds, sands, tuffs and exhalites.

Has lode gold mineralization been involved in this deformation? The answer is yes!

Major and parasitic (minor) folds, and boudins are present. Chapters 7 and 8 clearly demonstrate this primary folding and boudinaging.  Its influence is the same on all existing layers from volcanic tuffs, iron formation, massive sulphide and lode gold bands, whether or not they are mineralized. During deformation the primary textures are preserved showing that remobilization does not take place, only deformation!

Figure 4: Folded band of layered quartz and iron carbonate, Miller Lake Gold District, Ecum Secum Map Area. (Copyright Derek McBride)

In summary the book presents data that lode gold systems have the same syngenetic characteristics as VMS deposits and have been subjected to the same primary deformation events.  A syngenetic origin explains lode gold deposits far better than a shear zone model.

The book’s goal is to provide a more comprehensive, historical perspective for all those geologists who want to fully understand lode gold deposits.

the metallogeny of lode gold deposits

To access this book on ScienceDirect, click here.

To purchase your own copy and other related titles, visit Elsevier Store and save up to 30% using discount code STC317

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