Download Online Resource 1. Petrography of intrusives intercepted at depth

Online Resource 1. Petrography of intrusives intercepted at depth
Rojo Grande granite:
Leucocratic, monzogranite rock with color index between 5.3 and 6.7; present phaneritic, equigranular,
holocrystalline and alotriomorphic textures. The major constituents are anhedral quartz, anhedral potassium
feldspar with perthitic texture, subhedral plagioclase with sericite alteration. Tabular biotite is observed,
locally is present in skeletal crystals with replacements of secondary biotite and edges filled with opaque
minerals (magnetite). Secondary biotite is also observed in aggregates associated to anhydrite product of
hydrothermal alteration. The accessory minerals are: titanite in perfect rhombic section and subhedral crystals,
often associated with secondary biotite, chlorite and opaques, (100 - 400μ); magnetite and hematite in cubic,
subhedral and anhedral crystals (100 - 400μ), and locally ilmenite exsolutions in hematite in smaller grains
50-200μ are present. Apatite and zircon are also accessory minerals. This unit presents homogeneous but poor
distribution of chalcopyrite with size between 10-20μ. Present abundant mineralization as sheeted veins and
strong stockworks with bornite-digenite-chalcopyrite near contacts with younger porphyric units and
hydrothermal breccias. At depths greater than 1000m is observed with low mineralization.
Clara granodiorite:
Granodiorite phaneritic locally porphyritic rock, holocrystalline, leucocratic with color index between 6 and
9, macroscopically is known for aggregates of irregular biotite up to 3mm, euhedral amphibole altered to
biotite up to 8mm and prismatic plagioclase surrounded by potassium feldspar. The main minerals are
plagioclase with patchy texture and oscillatory zoning, locally mirmekitic with fine anhedral quartz
inclusions, recrystallizations at edges and moderate sericitization. The K-feldspar occurs in anhedral crystals
with perthitic texture. Anhedral quartz is observed filling interstices. The minor constituents are biotite,
anhedral with irregular borders or skeletal texture with alteration to secondary biotite and chlorite. Amphibole
is seen mainly as skeletons with recrystallization of biotite and slight alteration to chlorite, is associated with
titanite, quartz and magnetite. Titanite is an accessory mineral and occurs in subhedral crystals or fragments
with sizes between 100-1500μ, present fractures and borders with magnetite and rutile. Zircons are prismatic
to subhedral accesory minerals; size is between 10μ to 30μ. Some euhedral prismatic apatites are usually
observed included in plagioclase (sizes 0,5μ-2μ). Subhedral associations of hematite-magnetite are mainly
related to the biotite and titanite, size varies between 0,5μ-2μ.
Mesocratic Clara granodiorite:
Is a coarse-grained equigranular rock with variable composition characterized by the presence of large
euhedral hornblende crystals up to 20mm, locally replaced by secondary biotite and chlorite. Consisting of
11-18% of hornblende, subhedral plagioclase (20-34%), biotite (8-12%), potassium feldspar (10-15%),
quartz (10-18%), magnetite (2%) and accessory minerals like relictic titanite, apatite and rutile (0,5-1%).
El Abra porphyries:
This bodies form a group of leucocratic porphyry dikes, near vertical, with color index between 3.5 and 4.7.
Modal composition varies from andesite to dacite. This set of intrusive is characterized by the presence of
quartz eyes, quartz phenocrysts with ameoboidal appearance and polycrystalline aggregates of quartz ±
potassium feldspar ± bornite ± chalcopyrite ± pyrite filling miarolitic cavities and Unidirectional
Solidification Textures (UST) mainly in apical zones and borders of small dykes. Phenocrysts are mainly of
plagioclase (43-50%, Modal composition QEMSCAN) with oscillatory zoning in a microfelsic matrix. These
rocks are sub-divided into the following compositional categories: andesite porphyry, dacite porphyry and
quartz-latite porphyry, however slight textural and compositional variations are observed within these groups.
Andesite porphyries:

EA-561, EA-651: mesocratic, holocrystalline, porphyritic unit. Modal composition is andesite.
Phenocrysts (47-62%), present sizes between 1 to 4mm, mainly are subhedral to euhedral plagioclase with
sericitization, surrounded by potassic feldspars. Quartz phenocrysts of minor size (0,5-2mm) with amoeboid
texture and polycrystalline aggregates with biotite are also observed. Biotite is poor like phenocrysts and
present secondary biotite aggregates, however is abundant in the matrix. Magnetite-hematite are accessory
minerals disseminated in the matrix and filling fractures. Bornite, chalcocite, digenite and chalcopyrite occur
disseminated and locally “mirmekitic” texture between bornite-chalcocite is observed. This unit is
volumetrically minor, form dykes intruding Clara granodiorite and is present like small xenoliths in dacite and
rhyolite porphyries. Quartz-rich veinlets with biotite-bornite-chalcopyrite and potassium feldspar halos crosscut this unit.
 EA-1047: the modal composition of this porphyry is located in the limit between quartz-monzonite to
quartz-monzodiorite, is characterized by a low matrix content (<30%), high content of potassic feldspar
(20%) and plagioclase
phenocrysts (46%), phenocrysts of quartz are scares (<9%) with embayment of
matrix, biotite is a minor constituent (up to 4%) and not have amphibole (QEMSCAN modal composition
0.03%). The matrix is microfelsic with grain size between 200-600μ and phenocrysts have sizes between
600μ to 3,5mm. Fine quartz-rich veinlets with bornite-digenite-chalcopyrite±biotite and fine potassic feldspar
discontinuous and irregular halos cross-cut this unit. Small anhedral crystals of bornite-digenite associations
(70-150µ), subhedral chalcopyrite (10-20µ) associated to hematite-magnetite are disseminated close to
veinlets.
Dacite porphyries:
 EA-874, EA-1075, EA-1086: dacitic rock, consists of 27-30% of microfelsic (100 to 300μ) matrix and
65-68% of phenocrysts with sizes between 300μ to 3mm. This variety predominates in the study area; is
distinguished by a low content of amphibole <0,5%, biotite content between 1.5 to 2%; and titanite, apatite,
rutile and magnetite as accessory minerals. Quartz-rich A and AB type veinlets, with associations of biotite ±
anhydrite ± bornite ± chalcopyrite ± molybdenite ± pyrite and B veinlets with quartz±bornite<chalcopyrite
and discontinues potassic feldspar halos, are cross-cut by late D veinlets with chalcopyrite and quartz-sericite
halos with disseminate chalcopyrite.
 EA-662, EA 1203: dacite rock, consisting of 36 to 46% of microfelsic matrix with grain size between 50150 µ and 38-48% of phenocrysts (300 μ -2mm). This variety presents a high content of biotite (2-3%) and
amphibole (up to 1%). Accessory minerals are titanite, and apatite, magnetite is observed principally
associated to amphibole. Locally fine quartz-rich veinlets with chalcopyrite-magnetite and potassium feldspar
halos are observed. Close to contacts with other porphyry phases present “stockworks” of AB type veinlets
with chalcopyrite ± bornite ± molybdenite.
 EA-1535: based on modal composition is a dacite rock, constituted by 34% of microfelsic matrix with
size between 125 to 400μ and 59% of phenocrysts with sizes between 500μ to 3mm. Differs from other dacite
porphyries by high content of biotite (up to 3%), amphibole (up to 2%), coarser matrix and higher content of
phenocrysts. It occurs as dykes intruding Clara granodiorite and as matrix of magmatic breccias, including
clasts of other phases of dacite porphyry and clasts or fragments of quartz veinlets without mineralization.
Present scarce A, AB, B and D veinlets and develops a "stockwork" of moderate intensity restricted to
contacts with other intra-mineral units.
 EA-1284, EA-901, EA-862: modal composition locates these porphyries in the dacite field. Constituted
by 24-29% of microfelsic matrix (50-200 µ) and 66 to 70% of phenocrysts, these are principally subhedral
plagioclase, potassic feldspar and subrounded quartz with embayments of the matrix. Biotite content is
between 2-3% and amphibole modal QEMSCAN compositions is <0.2%. Quartz aggregates are common
(quartz eyes). These porphyries are characterized by a wide textural variation, large dykes (>10m) to depths
of 500m approximately present coarse porphyry texture to the central part of the intrusion and progressively
change to a micrographic texture recognized like leucogranite phase in the drillhole mapping. Stockworks
with quartz-rich veinlets A and AB types with anhydrite+biotite+bornite+digenite+chalcopyrite are observed,
to the edge of dykes is common the presence of sheeted veins associated to leucogranite phase.
Late quartz-monzonite porphyry (EA-660):
Quartz-monzonite rock, mesocratic, holocrystalline and porphyritic. Consisting of 53% of matrix and 37 % of
phenocrysts. Matrix present a very fine size between 20-80µ, constituted by plagiolcase, quartz and potassic
feldspar. Phenocrysts present sizes between 200-600µ, primarily subrounded plagioclase and fragments with
strong sericitization and reabsorption rims, biotite and amphibole are in proportions <3% and present
alteration to chlorite-epidote, accessory minerals are titanite and apatite. Zircon, rutile and chalcopyrite
inclusions are observed associated to chlorite aggregates. Mineralization is scares, principally
chalcopyrite+pyrite distributed in the matrix. This unit forms a series of late polimigtic breccias to the south
section of the current pit.
Leucogranite (EA-447, EA577):
Syenogranitic rock, leucocratic with color index <1, texture is holocrystalline, alotriomorphic, from aplitic to
fine-granular. Biotite is a minor constituent, present as aggregates of secondary biotite and associated to
accessory minerals like titanite, zircon and magnetite. Disseminated mineralization is observed in associations
of bornite-digenite replaced by covellite and chalcopyrite. Quartz-rich veinlets A and B type are observed
with bornite+digenite+chalcopyrite.