## 2 Geology of the Study Area  
The study area is a granite quarry located in the municipality of Budduso, in the Sardinia Region, Italy (Figure 1). In this quarry, which has been in operation for more than 40 years, substantial quantities of granite waste have accumulated, forming clearly distinguishable heaps even from several km away.  
From a geological perspective, the island of Sardinia, together with Corsica, constitute a 30 kilometer-thick crustal block within the Southern European Variscan belt in the western Mediterranean Sea [22]. The Variscan basement, which was produced during the collision between the northern Armorica and southern Gondwana, is composed of low- to high-grade metamorphic rocks deformed during the Early Carboniferous as well as of Permo-Carboniferous igneous bodies [23]. The large Corsica-Sardinia batholith (C-SB) [24], formed during the post-collisional stage, results from the superposition of several magmatic events spanning the 340-280 Ma age range [25; 26]. Three magmatic suites have been distinguished within the C-SB [27; 28]:  
1. Suite U1: an early Mg-K calc-alkaline suite, outcropping exclusively in Corsica, composed of monzodirites, monzonites, and subordinate ultrapotassic mafic rocks. The U1 suite was emplaced in a compressional setting [29; 30], from 345 to about 337 Ma [26];
2. Suite U2: a composite, and peraluminous to slightly peraluminous high-K calc-alkaline suite composed of granodirites and monzogranites with subordinate tholeitic gabbros. This suite is widespread in both Corsica and Sardinia, where it covers an area of \(\sim\)6000 km\({}^{2}\), accounting for \(\sim\)80% of the batholith's exposure [31]. The U2 high-K calc-alkaline magmatism lasted from 322 to 285 Ma [26; 32; 33; 34];  
Figure 1: Satellite image of the Budduso quarry area. Bottom left: a view of one of the granite waste heaps within the quarry.  
Suite U3: a suite consisting of metaluminous calc-alkaline to calcic gabbros and alkaline volcanic complexes ranging in composition from basalt to rhyolite. This suite represents the end of the magmatic cycle, between 290 and 260 Ma [26; 33].  
With specific reference to the study area, in previous works the granite complex was attributed to the high-K calc-alkaline plutonic association U2. This area is characterized by the presence of the so-called Buddso plutton [35]. This latter is a medium-size pluton, with an area of approximately 70 km\({}^{2}\)[23], outcropping in the NE Sardinia, which consists of tonalites, granodiorites, and monozgranites containing widespread microgranular mafic enclaves [27; 36]. As for the ages of the pluton emplacement, studies are fairly agreed in dating it between 286 and 281 Ma [34; 37].  
The Buddso plutton has been described, by [PERSON] and [PERSON] [35], as a pluton formed by three nested rock units:  
* The Outer Unit (Ou) is characterized by banded, medium- to coarse-grained, porphyitic biotite grandiodirites and tonalites, occasionally containing hornblende (Ou1), as well as porphyitic biotite monozgranites (Ou2). These lithologies frequently include abundant mafic enclaves, ranging in size from centimeters to decimeters, composed of dioritic to tonalitic material.
* The Middle Unit (Mu) comprises layered, medium-grained, porphyitic biotite monozgranites with sparse mafic enclaves that vary from decimeter to meter scale. Two subunits were identified within this unit, differentiated by biotite content: the external subunit (Mu1) has a higher biotite concentration than the internal subunit (Mu2). Near the boundary with the Inner Unit, large bodies of quartz diorites or tonalites are found in association with heterogeneous monozgranites.
* The Inner Unit (lu) is composed of homogeneous, coarse-grained, leucocratic monozgranites that generally lack phenocrystals. Mafic enclaves are either scarce or completely absent in this unit.