Structural Control on the Formation of Pb-Zn Deposits: An Example from the Pyrenean Axial Zone

Abstract

Pb-Zn deposits and specifically Sedimentary-Exhalative (SEDEX) deposits are frequently found in deformed and/or metamorphosed geological terranes. Ore bodies structure is generally difficult to observe and its relationships to the regional structural framework is often lacking. In the Pyrenean Axial Zone (PAZ), the main Pb-Zn mineralizations are commonly considered as Ordovician SEDEX deposits in the literature. New structural field analyzes focusing on the relations between mineralization and regional structures allowed us to classify these Pb-Zn mineralizations into three types: (I) Type 1 corresponds to minor disseminated mineralization, probably syngenetic and from an exhalative source. (II) Type 2a is a stratabound mineralization, epigenetic and synchronous to the Variscan D1 regional deformation event and (III) Type 2b is a vein mineralization, epigenetic and synchronous to the late Variscan D2 regional deformation event. Structural control appears to be a key parameter in concentrating Pb-Zn in the PAZ, as mineralizations occur associated to fold hinges, cleavage, and/or faults. Here we show that the main exploited type 2a and type 2b Pb-Zn mineralizations are intimately controlled by Variscan tectonics. This study demonstrates the predominant role of structural study for unraveling the formation of Pb-Zn deposits especially in deformed/metamorphosed terranes.

Behavior of critical metals in metamorphosed Pb-Zn ore deposits: example from the Pyrenean Axial Zone

“…400 kt of Zn and 180 kt of Pb (BRGM 1984;Ovejero Zappino 1991). Three types of Pb-Zn mineralization are described in Cugerone et al (2018b). Type 1 is minor, disseminated, and laminated mineralization, probably associated to sedimentation during Cambro-Ordovician and Devonian times (Fig.…”

“…It can also be associated to fault damaged zones in Late-Ordovician marble in Margalida ( Fig. 1b; Cugerone et al 2018b).…”

“…Type 2b (Fig. 1) is epigenetic vein mineralization probably late, or post-dating, the D /M deformation event (Cugerone et al 2018b). Pb-Zn mineralization is structurally controlled and occurs as vertical decimetric-sized veins parallel to S cleavage, which locally intersect type 2a mineralization.…”

“…No alteration halo has been observed along the contact with the host-rock. Type 2b mineralization cuts Late-Variscan aplitic intrusions and is affected by a cleavage parallel to the Late-Variscan S cleavage in the host rock (Cugerone et al 2018b). We have studied samples from type 2b Pale Bidau, Arre, and Anglas deposits hosted in calcschists ( Fig.…”

Editorial for Special Issue “Structural Control of Mineral Deposits: Theory and Reality”

“…Three publications of this volume explore the development of mineralization in the specific context of orogenic domains. Cugerone et al [18] offer a detailed study of a rather complex Pb-Zn mineralisation developed within the orogenic Hercynian Pyrenees during two mineralization stages, each of them linked with a deformational event. The syntectonic primary mineralization is remobilized and helps the formation of the second one.…”