[en] Unconformity-type uranium deposits in the Athabasca Basin (Canada) are commonly hosted and surrounded by breccia bodies in quartzose sandstones. In order to understand the mechanisms of breccia formation and their significance for the genesis of uranium deposits, the breccia associated with U mineralizations of the Shea Creek prospect and Sue C open pit, and with the Y-REE-U mineralization of the Maw Zone were studied. Structural mapping and 3D modeling evidence the control of breccia geometries by reverse faults that are graphite-rich in the basement. The study of mineral paragenesis and calculations of U-Pb chemical ages at Shea Creek reveal 3 breccia phases with sudoite-dravite, Fe-chlorite and hematite-siderite cements. These breccia developed over more than 1 Ga respectively during 3 stages of tectonic reactivations and/or basin uplift mainly between 1.52 and 1.25 Ga during the main event of primary uranium deposition and at about 900 and 350 Ma during phases of uranium remobilization. The breccia coeval with the genesis of the primary mineralization developed in 3 stages characterized by fractal analysis of fragment shapes expressing their degree of maturity. The first stage of breccia formation has been triggered by a reactivation of graphite-rich reverse faults inducing localized tectonic fracturing in the core of faults and widespread hydraulic fracturing in early silicified zones. The second stage corresponds to quartz dissolution due to the vertical circulation of a basement fluid under-saturated relative to quartz in fractured sandstones. Calculated minimum fluid/rock ratios are very high with values of 3,000 at the Maw Zone and 38,000 in the Sue 'zones a boules' reflecting the decrease of dissolution intensity with the increase of distance to the unconformity. The minimum volume of basement fluids that have circulated through the breccia is about 1 km³. Mass balance calculations show an input of U, V, Mg, B, Al, K, Bi, Ni, Co, Mo, As, S, W, Zn, Y and REE, in accordance with the new formation of illite, Mg-rich sudoite and dravite and with the polymetallic sandstone-hosted mineralization. The third stage is expressed by gravity-driven collapse phenomenons resulting from the cavities created by quartz dissolution. In 'zones a boules' developed in the core of faults, it is the tectonic contraction that progressively closed the open spaces formed by quartz dissolution. Volume loss values reach 90 % in zones of intense dissolution close to the unconformity. In steeply dipping fault zones, collapse propagated up to more than 250 m above the unconformity as observed at the Maw Zone, like in a karst. Uranium deposition induced by mixing of the reducing basement fluid under-saturated relative to quartz (> 250 deg C) with diagenetic oxidizing basin fluids (< 240 deg C) occurred during about several million years, simultaneously with quartz dissolution providing the space needed to form the massive mineralizations. (author)