Importance of cymoid loops and implications for exploration and development of epithermal gold-silver veins in the Gold Circle district, Midas, Nevada

The Gold Circle (Midas) district, Elko County, Nevada, contains numerous
well-developed examples of cymoid loops, which significantly affected the formation
of veins, and influence geotechnical aspects of mine development and economic exploitation
of ore.
The first use of the term cymoid loop to describe veins was suggested by Dr. Kirk
Bryan as an analogy to the architectural form used to describe certain shapes of molding
(McKinstry, 1948). In general, a cymoid loop can be described as a vein or structure
that branches and swerves fromits course only to reunite and return to its general
course, whereby enclosing a doubly-convex lens of wall rock (McKinstry, 1948). Ultimately,
by taking either branch of the structure one will return to the same general
trend as one started. Cymoid loops have been described in many well known gold and
silver vein districts, such as Grass Valley, Calif. (Johnston, 1940), Pachuca, Mexico
(Thornburg, 1945) and the Hauraki goldfield of New Zealand (Begbie, Spörli and
Mauk, 2007).