Arenal Deeps is an Au mine located near Minas de Corrales, Uruguay, which was exploited via an open pit operation from 2004 until 2009 and underground since then, using both inclined room and pillar and transversal stoping methods. The progression of mining activities (down to ~320m BGS) has led to an evergrowing complexity in the geometry of the mine, which cannot be adequately assessed solely with empirical design methods. This work presents a case study in which empirical and numerical methods were integrated to assess the stability of a stope roof and adjoining pillar. Empirical methods enabled straightforward determination of the need to include an intermediate pillar. A 3D boundary element model indicated that stress concentration in the roof was the main driver for instability. The 2D finite element model provided a FoS for roof failure of 1.20, considered adequate given the conservative plane-strain hypothesis it entails and geomechanical uncertainty.


Arenal is a mesothermal epigenetic Au deposit located 400 km North of Montevideo, Uruguay, hosted within basement amphibolite facies gneissic rocks inside the Proterozoic greenstone terrain known as the Isla Cristalina (Golder 2009).

Mineralization is well constrained by upper (hangingwall) and lower (footwall) fault contacts within the 50–100 m wide, east-west and northwest trending Rivera Shear zone. It has drill-defined dimensions of 900 m along strike at surface and >700 m down plunge, dipping moderately at 40–50 degrees to the south and steepening to more than 70 degrees at depth.

Structures are interpreted to be reverse faults and thrusts that predate the Rivera Shear. The main alteration assemblage associated with gold mineralization within the hosting structures comprises chlorite-(epidote)-carbonate-sericite-silica-pyrite.

The Arenal deposit was exploited via an open pit operation from 2004 until 2009. The final pit is ~500 m long, 330 m wide and 159 m deep, having an inter-ramp angle of 47°-56°. The Arenal Deeps underground mine is a combination of six inclined room and pillar (IRP) sub-levels and seven transversal stoping (TS) sublevels, developed through a ramp that starts on the north wall of the pit, 98 m below surface, and plunges 240 m further below at a mean inclination of 8.5%.

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