## 1 Introduction  
The SW of the Ciudad Real Province (Castilla-La Mancha, south-central Spain) is particularly well-known from the geological and mining points of view, mainly as the location of an important Hg mining deposit, the Almaden district, which has historically produced one-third of the total industrial production of this element ([1] among others). The district is restricted to the so-called Almaden syncline, constituted by the Paleozoic (Lower Ordovician to Upper Devonian) (meta)sedimentary rocks with the frequent presence of -mafic magmatic rocks, both volcanic and subvolcanic [2; 3; 4; 5]. The Guadalmez syncline extends adjacent and to the south of this syncline, with some minor Sb deposits that were exploited in the early 20 th century [6; 7], and, from the geological point of view, is relatively similar to the Almaden syncline but includes a more complete stratigraphic succession and a lesser abundance of magmatic rocks [8]. Furthermore, the Alcudia Anticline extends between these two synclines and is the site of the Valle de Alcudia Pb-Zn-Ag mining district, including a significant number of small-to-medium-sized vein deposits exploited from Roman times to the mid-20 th century [9]. The tectonic structure of the area corresponds to the effects of the Variscan orogenic event, developed in Devonian-Carboniferous times (370-290 Ma), producing the folding and faulting of the area and low-grade metamorphism [10]. In more detail, the Almaden and Guadalmez synclines are \(\sim\)N120\({}^{\circ}\) E tending tectonic structures. Their stratigraphic succession includes four quartzitic layers of decametric thickness separated by sequences of shales and/or alternations of shales and quartzites (ASQ) (Figure 1). These sequences are among the most complete records of the Paleozoic in the Iberian Peninsula, from the Lower Ordovician to the Lower Carboniferous [3; 4; 8; 11]. There is a conspicuous presence of igneous mafic rocks at the Almaden syncline, particularly in the Upper Devonian, constituting an authentic volcano-sedimentary sequence [12]. It is noteworthy that in lower stratigraphic levels, the presence of these rocks is sporadic in time and space, in the form of sills and dikes of basaltic rocks (rarely identified as concordant bodies undoubtedly interpretable as lava flows), pipe-like structures filled by mafic pyroclasts with ultramafic enclaves (the so-called _Frailesca_ rock), and sills and lopolith-shaped bodies of doleritic rocks [5; 13]. In the Guadalmez syncline, the presence of magmatic rocks is minor with respect to Almaden, with only the sporadic presence of diabase in irregular masses, intruded with preference in the Silurian shales [14]. [PERSON] et al. (2013) [13] and [PERSON] et al. (2022) [15] characterize these rocks as two magmatic series of alkaline affinity for the volcanic varieties present in Almaden (ALK-1) and of tholeiitic affinity to the diabase present in both synclines (THOL-1). The Almaden syncline hosts the huge Almaden mercury mining district [1; 15], interpreted as genetically related to the ALK-1 episode [5], while the Guadalmez syncline hosts several small Sb mineralizations, related, at least geographically, to the THOL-1 diabases. Regional soil geochemistry, which involves soil samples collected over wide grids, has its main application in the determination of baseline and reference levels for the different elements and usually allows for the characterization of the differential composition and variability of the lithologies represented over a broad area. However, it also allows for the identification of large-extension anomalies, which can correspond to geogenic variations, as well as to anthropogenic contributions. The best examples of regional soil geochemistry datasets correspond to a continental or national scale geochemical atlas, such as those for Europe [16] or Spain [17], among many others.