PART III Conclusions and Recommendations Chapter１ Conclusion (1) Satellite Image Interpretation As a result of rationing of satellite image interpretation of this year, a sizable anomaly of R21 (iron oxide index) is distributed in the quadrangle of 32-q, 32-r and 31-r in the east of the survey area. The anomaly is tend to be larger in the geological units of PN-ta (Holocene pyroclastics) and tend to be smaller in Ks-ti (upper Cretaceous intrusives), JK-yu (Jurassic to Cretaceous sediments), Ks-se (upper Cretaceous sediments) and Ks-ar (upper Cretaceous sediments). A sizable anomaly of R57 (clay mineral index) is distributed in the quadrangle of 32-q and 32-r in the east of the survey area, although the anomalies are distributed all over the survey area. They tend to be concentrated in the geological units of PeB (pre Cambrian metamorphics), JK- yu (Jurassic to Cretaceous sediments), Ks-ti (upper Cretaceous intrusives), PN-ta (Neogene volcanics), NQ-ba (Quaternary volcanics) and Q-and (Holocene pyroclastics). Conspicuous anomalies are located in alluvium and along the existing river. In the east of the area, conspicuous anomalies are located in the units of JK-yu, PN-ta, QN-ba and Q-and. The lineaments of Andes trend (NW-SE) are predominantly distributed in the survey area. However, the lineament of E-W is predominantly distributed in the quadrangles 32-o and 32-p. This is probably due to the effect of Abancay Deflection which deflect the trend of strata to E- W from Andes trend (NW-SE) located to the north of the survey area. Pattern of lineament density is generally conformable to the above-mentioned Andean trend and the deflection. High lineament density area is coinciding with the area of the deflection. In comparison with geologic units, the lineament density tend to be lower in the young geological unit e.g. Tertiary system and Quaternary system, while lineament density tend to be higher in the old geologic units, consisting of Paleozoic and Mesozoic formations. Relationship between the result of image interpretation and known mineral showings are summarized as follows: 1. Although the vein type ore deposit predominates over the survey area, a correlation between lineament density and distribution of ore deposits is not clear. 2. Between the location of vein type deposits and indices of iron oxide and clay mineral, the following relationship is recognized in general. 1) In case of ore deposit is located in Cenozoic formation, the ore deposit is accompanied by either iron oxide index or clay mineral index in any case. 2) In case ore deposit is located in Mesozoic or Paleozoic formation, the ore deposit is accompanied by either index as the case may be. 3. Location of manto type ore deposit coincides with the area of high lineament density. 4. Neither iron oxide index nor clay mineral index appear in the area of manto type ore deposit. 5. Ore deposit of disseminated type and stockwork type is located around the area of relatively high lineament density. 6. Ore deposit of disseminated type and stockwork type is commonly accompanied by either iron oxide index or clay mineral index even though they are weak. Particularly this is clear in the case of ore deposit occurs in Cenozoic formation. (2) Existing Data Analysis Metamorphic rocks, sedimentary rocks and volcanic rocks of pre Cambrian to Quaternary age, elongating northeast to southwest, are widely distributed in the survey area. Penetrating them, intrusive rocks of Ordovician to Silurian, Cretaceous to Paleogene and Neogene in age are located. In the southwest and east of the survey area pre-Cambrian metamorphics are - 119 - distributed, and the younger sediments and volcanics are orderly distributed to the north. The area is divided into the metallogenic zones of Paracas-Chala, Mala-Nazca, Nazca-Ocoña and Puquio-Caylloma from the Pacific Ocean side to inland. In comparison with the previous Peruvian metallogenic provinces, Paracas-Chala metallogenic zone corresponds to the cupreous sub-province, the iron ore zone. Mala-Nazca metallogenic zone corresponds to the cupreous sub-province, the copper ore zone, Nazca-Ocoña metallogenic zone corresponds to the cupreous sub-province, the gold ore zone and Puquio-Caylloma metallogenic zone corresponds to the polymetallic sub-province respectively. Number of ore deposits and mineral showings of this area totaled 260. Among them 238 is vein type deposit, of which 172 is gold vein or gold copper vein, that shows the character of Nazca- Ocoña metallogenic zone. 56 vein type copper deposits show the character of Mala-Nazca metallogenic zone. Manto type deposits totaled 15, of which 12 are manto type iron deposits and two are manto type iron copper deposits. Ore deposits of the Marcona mine, the only producer of iron ore in Peru, are composed of the above two types of manto type deposits. Around the Marcona mine six iron ore veins and three iron copper ore veins are known to occur which show the character of Paracas-Chala metallogenic zone. Aside from them the existence of four dissemination type deposits and three stockwork type deposits is known. Considering mineral paragenesis of those showings, it is very meaningful that a few mineral showings with only gold occur in volcanic rock of Cenozoic age. That suggest the existence of gold mineralization related to young volcanism can be expected. Since the host rock of these showings are the Tacaza group and the Camaná group of lower Miocene age, the Barroso group of Pleistocene age, the gold mineralization seems to have taken place continuously from Miocene to Holocene. The existence of stratabound type ore deposit in the area of gold vein in Mesozoic sedimentary rocks is a subject worth studying as there is a description of a small manto type copper gold showing in the Seraj formation of Mesozoic age. Metallogenetic study on those ore deposits and mineral showings except for the Marcona mine has not been conducted. From the existing data and distribution of mineral showings, mineralization in the survey area is classified into the following types. · Manto type and vein type iron (copper) deposits related to andesitic intrusives of late Mesozoic age. · Gold vein, gold-copper vein and copper vein related to the Coastal Batholith of late Cretaceous to Paleogene age. · Vein type, dissemination type and stockwork type gold deposit related to volcanic rocks of Miocene to Holocene age. Among the above types of mineralization, the target of this survey is to be placed primarily on the gold deposit related to volcanics of Miocene to Holocene age and secondarily the gold vein related to the Coastal Batholith. (3) Overall Analysis Based on the results of the satellite image analysis and existing data analysis, 1) Iron oxide index anomaly obtained by satellite image analysis 2) Clay mineral index anomaly obtained by satellite image analysis 3) Density of lineament 4) Distribution of volcanic rocks of Miocene to Pleistocene 5) Distribution of the Guaneros formation, the Yura group and the Casma group of Mesozoic age 6) Location of known mineral showings From the above basis the following five area s are selected as a promising area. - 120 - ① Nazca area ② Tocota area ③ Chuquibamba area ④ Andagua area ⑤ Orcopampa area Basis of the judgment is indicated in the following table. Table of Promising Area Area Center R21 R57 Lineament Objective Known Coordinates (Iron (Clay Mineral Density Country Rocks Indication Oxide Index) Index) ①Nazca 14ﾟ25’S Weak near Small scaled in High density JK-yu Au Vein type 75ﾟ15’W Yura Group Yura G., trends Summit (Yura Group) NW-SE ②Tocota 15ﾟ40’S Small scaled Medium scaled High density Js-gu Au Vein type 74ﾟ10’W within Guanero along fault 3 summits (Guaneros F.) s Formation system in Guan JK-yu eros F. (Yura Group) ③Chuqui- 15ﾟ40’S Large scaled Small scaled Saddle PN-ta Au bamba 72ﾟ45’W within Tacaza G in Tacaza G. Between high (Tacaza G.) Dissemination roup and and Barroso G. density summi NQ-ba type continue to Barr Overlap to R21 ts （Barroso G.） oso Group in part ④Andagua 15ﾟ30’S Large scaled Small scaled High density PN-ta nothing 72ﾟ25’W within Tacaza G in Tacaza G. 2 summits (Tacaza G.) roup and and Barroso G. NQ-ba continue to Barr Overlap to R21 （Barroso G.） oso Group in part ⑤Orcopampa 15ﾟ20’S Large scaled Medium scaled High density PN-ta Au Vein type 72ﾟ15’W within Tacaza G in Tacaza G. 4 summits (Tacaza G.) Dissemination roup and and Barroso G. NQ-ba type continue to Barr Overlap to R21 （Barroso G.） Stockwork oso Group in part type - 121 - Chapter ２ Recommendation in Future As this year’s survey and analysis revealed that the survey area is promising in potential for mineral resources, a field survey to confirm the potential is to be conducted in future. In conducting the ground survey it is important not only to make a correct interpretation on each geological fact, but also to consider the position of each geological fact in the whole geological setting of the area. Understanding of the regional geological character is also important. The main objects of survey in the selected district are described as follows; ① Nazca area The district is widely underlain by the Yura group of Mesozoic age. Intrusive rock of the Tibaya Super unit is extensively distributed in the north and south of the district. Occurrence of a number of vein type gold deposits is known. Therefore, in order to obtain the data of gangue mineral composition, formation temperature of ore deposits, wall rock alteration, a field survey is to be conducted. Then the possibility of existence of concealed stratabound deposit is to be studied.