New metallogenic approaches to the Coastal Batholith, Arequipa segment between 15° and 16°30' South latitude, Peru
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Abstract:
The mapping of intrusive rocks from the Arequipa segment of the Coastal Batholith was complemented by detailed petrographic studies and U-Pb zircon ages. The results were analyzed and grouped into seven stages and four cycles. Each stage shows unique magmatic volumes, and the landform finds expression in batholiths and stocks. Cycles Ⅰ and Ⅱ represent the stages of Jurassic magmatism (201~145Ma), the magmatic differentiation grades from gabbros to granites. Cycles Ⅲ and Ⅳ represent the stages of Cretaceous magmatism, the magmatic differentiation varies from tonalites to monzogranites, diorites to granodiorites and from tonalites to granodiorites. In relation to the amphibole and biotite crystal population, the intrusives of the Cycle Ⅰ have abundant pyroxene and amphibole crystals, associated with Au-Fe mineralization; those of Cycle Ⅱ have abundant clustered amphibole crystals and in some cases are aligned or grouped biotite crystals and eventually hexagonal, associated with Cu-Au-Fe mineralization; those of Cycle Ⅲ have well developed isolated amphibole and biotites, and the intrusive rocks are associated with Au-Cu and Fe; those of Cycle Ⅳ have some amphibole and hexagonal biotite in separated form, and the intrusive rocks are more felsic and are associated with Cu-ZnAu-Ag-Fe and Cu-Au-Mo mineralization.
摘要:通过详细的岩相学和锆石U-Pb年龄的研究，秘鲁海岸岩基带阿雷基帕段的填图工作得到了补充，该岩基带岩浆活动可分为7个阶段和4个旋回，各阶段都显示出不同的岩浆容量，其地貌主要表现为岩基和岩脉。旋回Ⅰ和旋回Ⅱ代表侏罗纪岩浆活动阶段（201~145Ma），岩浆分异为辉长岩到花岗岩；旋回Ⅲ和旋回Ⅳ代表白垩纪岩浆，岩浆分异为英云闪长岩-二长花岗岩、闪长岩与花岗闪长岩及英云闪长岩-花岗闪长岩。对角闪石和黑云母矿物晶体的数量关系研究表明，旋回Ⅰ的侵入岩有大量辉石和角闪石结晶，并伴随金-铁成矿作用；旋回Ⅱ有大量的群集角闪石晶体和呈定向排列或群集的六边形黑云母，且伴随铜-金-铁成矿作用；旋回Ⅲ侵入岩内发育角闪石和黑云母，伴随着金-铜和铁成矿作用；旋回Ⅳ发育大量角闪石和六边形黑云母，岩石更偏长英质，并伴随铜-锌-金-银-铁和铜-金-钼成矿作用。
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Figure 1. Intrusive units of northern Arequipa segment.
(The legend shows the grouping of units based on absolute U-Pb ages)
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Figure 2. Generalized column of metamorphic, sedimentary, volcanic and intrusive rocks corresponding to the southern coast of Peru, Arequipa segment
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Figure 3. Model of magmatic differentiation of Cycle Ⅰ and Ⅱ (Jurassic intrusives), based on lithological variation and absolute age U-Pb
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图版 Ⅰ
图版 Ⅰ.
Jurassic intrusive samples: A1. Monzodiorite of the Torrecillas area; A2. Granodiorite with amphiboles; A3. Thin section (polarized light), quartz (cz), amphiboles (ANFs); B1. Diorite of the Chala area, amphibole and biotite crystals accumulated are observed; B2. Cuarzodiorite of the San Luis area, with amphibole crystals; B3. Thin section (polarized light), opaque (Ops), amphiboles (ANFs), plagioclase (PGLs); C1. Granodiorite crystals with some direction in relation to amphibole crystals; C2. Thin section (polarized light), plagioclase altered to sericite (PGLs-ser); C3. Monzogranite with isolated amphibole crystals; D1. Outcrop of Gabbro in the Cañahueca mountain, the contact with the granodiorite can be observed; D2, D3. Gabbro sample with banding compositional
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Figure 4. Model of magmatic differentiation of Cycles Ⅲ and Ⅳ (Cretaceous intrusives), based on lithological variation and U-Pb age
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图版Ⅱ
图版Ⅱ.
A1. Granodiorite of the Sondor town, isolated hexagonal biotite crystals are observed. To the right, thin section (polarized light), hexagonal biotite with reabsorption edge; B1. Granodiorite of the Cruzero and Pampahuasi town, diorite enclaves are observed; B2. Thin section (polarized light), amphibole crystals (ANFs) and plagioclase (PGLs); C1. Tonalite of the Calpa mine, crystals of scattered amphiboles are observed; C2. The Fe Acari mine diorite, developed amphibole crystals; C3. Thin section (polarized light), amphiboles are associated with opaque minerals and epoxide (ANFs-Ops-ep). Plagioclase are altered by micas and sericite (PGLs-MCs-ser); D1. Tonalite of the San Luis locality, crystals of developed amphiboles are observed. D2. Thin section (polarized light), Amphiboles chloritized with Fe oxides [ANFs (CLOs-OxsFe)], argillized potassium feldspar [FPKs (ARCs)], epidote (ep); D3. Granodiorite from the locality of Sacota, developed amphibole crystals (ANFs)
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Figure 5. Population of amphibole and biotite crystals of the intrusives of the Coastal Batholith, Arequipa segment, northern zone
(To right the magmatic cycles of intrusive rocks of the Coastal Batholith are shown in the study area. In relation to the amphibole crystals observed that there is a larger population in Cycles Ⅰ and Ⅱ, towards Cycles Ⅲ and Ⅳ decreases. In relation to the biotite crystals observed that it decreases towards the Cycle Ⅳ)
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Figure 6. Magmatic arcs based on plutonism cycles in Coastal Batholith, Arequipa segment
(Based on ages compiled by Torres et al.[20], Santos et al.[10-11], Huamán et al.[31], Demouy et al.[9], Boeckhout[8], Wasteneys et al.[17], Vidal et al.[32], Mukasa[7] and Cordani et al.[5]) IFS-Iquipi Fault System; CLLFS-Cincha Lluta Fault System; IFS-Ica Fault System
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