Spatial distribution pattern of seafloor hydrothermal vents to the southeastern Kueishan Tao offshore Taiwan Island

Investigations of the diffusion activities both within and outside the seafloor hydrothermal vents, as well as related mineral genesis, have been one of the key focuses of ocean biogeochemistry studies. Many hydrothermal vents are distributed close to the southern Okinawa Trough on the less-than-30-m deep shallow seafloor off Kueishan Tao, northeast of Taiwan Island. Investigations of temperature, pH and Eh at four depths of hydrothermal plume were carried out near Kueishan Tao at the white(24.83°N, 121.96°E) and yellow(24.83°N, 121.96°E) vents. An 87 h of temperature time series observation-undertaken near the white vent showed that tide is the main factor affecting the background environment. Based on the observed data, 3-dimensional sliced diffusion fields were obtained and analyzed. It was concluded that the plume diffused mainly from north to south due to ebb tide. The yellow vent's plume could effect as far as the white vent surface. From the temperature diffusion field, the vortices of the plume were observed. The Eh negative abnormality was a better indicator to search for hydrothermal plumes and locate hydrothermal vents than high temperature and low pH abnormalities.     

深海多金属硫化物瞬变电磁激电效应初探

瞬变电磁法是深海多金属硫化物勘探的有效手段。海底多金属硫化物中高品位的金属组分会引起极强的激电效应，且对瞬变电磁响应产生显著影响。本文通过实验室测量和数值模拟对深海多金属硫化物的激电效应进行了探讨和分析。首先对西南印度洋中脊热液区的岩矿石样品进行了较为系统的电性测试，典型硫化物的复电阻率在频率域有最大达160 mrad相位移动，时间域与频率域的测量结果表明，极化率参数可以很好地区分硫化矿物与围岩。利用Cole-Cole模型对实测复电阻率进行解释，得到复电阻率的特征参数，分析各参数与块状硫化物组分和结构的关系，并根据极化率参数对典型硫化物进行了分类。将典型硫化物的激电参数用于计算层状介质的瞬变电磁响应，计算结果表明，在海底多金属硫化物矿床瞬变电磁法响应的最佳观测时窗内可同时观测到激电效应的影响。虽然在采集时窗晚期瞬变响应发生畸变，但在信号接收早期，激电效应能有效增强瞬变电磁法对深海多金属硫化物的探测能力，为瞬变电磁实测数据提供解释依据。     

现代海底热液沉积物的硫同位素组成及其地质意义

共收集到现代海底热液沉积物的1264个硫同位素数据,结合我们对冲绳海槽Jade热液区和大西洋中脊TAG热液区中表层热液沉积物的硫同位素研究成果,对比分析了不同地质-构造环境中海底热液沉积物的硫同位素组成特征及其硫源问题.结果表明:(1)现代海底热液沉积物中硫化物的硫同位素组成集中分布在1‰～9‰之间,均值为4.5‰(n=1042),而硫酸盐矿物的硫同位素组成主要分布在19‰～24‰之间,均值为21.3‰(n=217);(2)无论在洋中脊还是在弧后盆地扩张中心,无沉积物覆盖热液活动区中热液沉积物与有沉积物覆盖热液活动区相比,其硫同位素组成的分布范围相对狭窄;(3)各热液活动区中硫化物硫同位素组成的不同,反映出各自硫源的差异性.无沉积物覆盖洋中脊中热液成因硫化物的硫主要来自玄武岩,部分来自海水,是玄武岩和海水硫酸盐中硫不同比例混合的结果,而在弧后盆地和有沉积物覆盖的洋中脊,除了火山岩以外,沉积物和有机质均可能为热液硫化物的形成提供硫;(4)现代海底热液沉积物硫同位素组成的变化和硫源的不同可能归因于海底热液体系中流体物理化学性质的变化、岩浆演化和构造-地质背景的不同.     

超慢速扩张环境下超镁铁质岩系统的热液硫化物成矿机理以及启示

西南印度洋63.5°E热液区是在超慢速扩张洋脊发现的首个超镁铁质岩热液系统。对取自该区的热液硫化物样品进行了系统的矿物学和地球化学分析，矿物学分析结果表明:该热液区硫化物为富Fe型高温硫化物，且经历了较深程度的氧化蚀变，大量中间态的Fe氧化物充填在硫化物矿物间的孔隙及内部解理中；这些硫化物相以白铁矿为主，其次是等轴古巴矿和少量铜蓝，缺乏黄铁矿、闪锌矿。据推断，该区的热液成矿作用分为4个阶段:低温白铁矿阶段→高温等轴古巴矿阶段→自形白铁矿阶段→后期海底风化阶段（少量铜蓝以及大量的Fe的羟氧化物）。与之相对应，地球化学分析结果表明这些硫化物的Fe含量较高（31.57%~44.59%），Cu含量次之（0.16%~7.24%），而Zn含量普遍较低（0.01%~0.11%）；微量元素较为富集Co（328×10-6~2 400×10-6）和Mn（48.5×10-6~1 730×10-6）。该区硫化物中较高含量的Fe、Co与超镁铁质岩热液系统相似，明显高于镁铁质岩热液系统。独特的热液硫化物矿物学特征和元素组成可能与该区普遍出露的地幔岩、橄榄岩蛇纹石化作用以及拆离断层的广泛发育的环境有关。     

Newly discovered hydrothermal fields along the ultraslow-spreading Southwest Indian Ridge around 63°E

The ultraslow-spreading Southwest Indian Ridge(SWIR) to the east of the Melville fracture zone is characterized by very low melt supply and intensive tectonic activity. Due to its weak thermal budget and extremely slow spreading rate, the easternmost SWIR was considered to be devoid of hydrothermal activity until the discovery of the inactive Mt. Jourdanne hydrothermal field(27°51′S, 63°56′E) in 1998. During the COMRA DY115-20 cruise in2009, two additional hydrothermal fields(i.e., the Tiancheng(27°51′S, 63°55′E) and Tianzuo(27°57′S, 63°32′E)fields) were discovered. Further detailed investigations of these two hydrothermal sites were conducted by Chinese manned submersible Jiaolong in 2014–2015. The Tiancheng filed can be characterized as a lowtemperature(up to 13.2°C) diffuse flow hydrothermal field, and is hosted by fractured basalts with hydrothermal fauna widespread on the seafloor. The Tianzuo hydrothermal field is an inactive sulfide field, which is hosted by ultramafic rocks and controlled by detachment fault. The discovery of the three hydrothermal fields around Segment #11 which receives more melt than the regional average, provided evidence for local enhanced magmatism providing heat source to drive hydrothermal circulation. We further imply that hydrothermal activity and sulfide deposits may be rather promising along the easternmost SWIR.     

New discovery of seafloor hydrothermal activity on the Indian Ocean Carlsberg Ridge and Southern North Atlantic Ridge—progress during the 26th Chinese COMRA cruise

The 26th Chinese COMRA (China Ocean Mineral Resources Research & Development Association) cruise was an important cruise. The Carlsberg Ridge (CR) of the Northwest Indian Ocean and the North Atlantic Ridge (NAR), in which less investigation has been carried out for hydrothermal activities, were investigated and studied during the first two legs of the 26th COMRA cruise. During the first leg, we found one hydrothermal activity field located in the CR at 3.5 -3.8 N on the Northwest Indian Ocean Ridge (NWIR), and sampled seafloor polymetallic sulfide deposits where only abnormalities were found before. During the second leg, we found a new hydrothermal anomaly field located in the NAR at 4 -7 N. The discovery of two hydrothermal and anomaly fields filled in the gap of hydrothermal investigation and study in the corresponding regions for China.     

Sulfur isotopic composition of modern seafloor hydrothermal sediment and its geological significance

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台湾龟山岛东南部海域白色热泉特征分析

海底热液活动及其周边环境的调查研究是海洋科学领域的热点之一。海底热液喷口环境的物理化学参数,尤其是浅水型热液,会受到潮汐变化的影响。台湾龟山岛靠近冲绳海槽南端分布有多处浅水型热液喷口(30m)。2010年5月,浙江大学、杭州电子科技大学和台湾中山大学对该海域实施了联合考察,利用电化学传感器获得了低温热液喷口(24.834 14°N,121.961 91°E)连续87h的温度和pH现场观测数据。基于Morlet复小波变换方法,分析了浅水型热液喷口的温度和pH现场观测时间序列的变化周期,并通过与当地潮汐记录数据作比较,获得了其与潮汐信号之间的潜在关系,证实了潮汐变化是海底白色热泉喷口物理化学参数现场观测最主要的影响因素。温度和pH现场观测数据经Morlet复小波变换后的小波系数分别存在规律的12.9h和12.5h变化周期,并且温度的小波系数在准半日周期尺度与潮汐高度呈负相关变化,相关系数为-0.89;pH的小波系数情况相反,相关系数为0.76。     

Mafic-hosted seafloor sulfide mineralization at the margin of a non-transform discontinuity on the southern mid-Atlantic ridge

Abstract

Mineralogical, geochemical and S-isotopic studies were carried out on seafloor massive sulfides (SMS) and hydrothermally altered rocks from the mafic-hosted TaiJi field (including TaiJi-1 and TaiJi-2 sites), which is located on the margin of a nontransform discontinuity (NTD) on the Southern Mid-Atlantic Ridge (SMAR). The main hydrothermal precipitates of TaiJi-1 were massive sulfides, while TaiJi-2 produced a large amount of semi-massive sulfides. Significant rock alteration is an important feature of this field, and large amounts of clay minerals (chlorite) occurred in the semi-massive sulfides. Geochemically, notable negative correlations were identified between rock forming elements (Mg) and major hydrothermal metal elements such as Zn?+?Cu and Co in semisulfides. Such mineralogical and geochemical characteristics, together with low Co/Ni ratio (similar to the surrounding rocks) of the semi-massive sulfides and the unique REE features of some altered rocks, tell us that the prominent mineralization mechanism for these semi-massive sulfides was probably related to rock mineralization. Thus, TaiJi-2 appears to differ significantly from the TaiJi-1 in terms of sulfide mineralization mechanism. Moreover, the TaiJi sulfides are remarkable for large δ³⁴S variation (7.2–15.3%). We suggest that seawater corrosion after sulfides precipitation were responsible for ³⁴S enrichment in sulfides. Furthermore, our work sheds some light on the comparison between TaiJi and other NTD-related fields along the Mid-Atlantic Ridge. We argue that rock mineralization may represent an important mineralization type in NTDs.     

“潜龙二号”自主水下机器人热液探测系统

“潜龙二号”水下自主航行器（QianlongⅡ AUV）为深海资源尤其是海底多金属硫化物调查而设计，其已在西南印度洋脊热液区进行成功的调查运用。本文系统地概述了“潜龙二号”的热液系统探测功能实现、数据管理、快速成图等工作；阐述了如何利用AUV转圈数据有效的校正载体对磁测干扰的。基于“潜龙二号”获取的热液异常，发展了热液喷口快速定位方法。以具体一潜次为例，系统地展示了热液探测数据的处理分析与热液异常定位工作，证实了该方法的有效性。     

海底热液活动的环境与产物

近23年的调查研究，使我们认识到分布于洋中脊、弧后盆地、岛弧和热点等环境的海底热液活动发育在多种围岩类型之上，包括超基性岩石、基性岩石、中性岩石、酸性岩石和沉积物。海底热液活动经历了岩浆去气作用、流体-岩石/沉积物相互作用和流体-海水混合，获取了岩浆、岩石、海水和沉积物的物质，构成了热液循环，产生了高温、低氧、高或低pH值、富含Fe、Mn、Cu、Zn、Pb、Hg、As等元素以及气体组分（甲烷、氢等）的喷口流体，影响了海水、沉积、岩石和生物环境，形成了热液柱、硫化物、含金属沉积物和蚀变岩石等热液产物，组成了海底热液系统。未来，促进海底热液活动探测技术和热液产物测试方法的发展，对海底热液区的岩石、喷口流体、热液柱、硫化物、含金属沉积物以及热液循环、生物活动的持续观测与研究，无疑将为人类探知海底地质过程及生命活动、保护海底热液环境和合理开发利用海底资源提供有力的工作支撑。     

西南印度洋49°～56°E洋脊段的热液羽状流:来自深水中的氦同位素异常证据

海水中的氦同位素能对海底热液活动进行有效示踪。本文对在西南印度洋49°~56°E洋脊段采集的5条CTD拖曳剖面共14件深水样品进行了氦氖同位素分析。通过分析水体中存在的氦同位素异常,探讨调查区热液异常的特征和热液羽状流的分布。分析表明,5条CTD剖面均存在δ3He异常,其中CTD7-2(位置:37.927°S、49.412°E,水深2 140m,离底高度100m)的δ3He值最大,达到49.2%。根据δ3He分布特征,认为调查区内存在至少6处热液羽状流,其中37.927°S、49.412°E以西数千米范围内可能存在海底热液喷口。     

洋中脊热液羽状流的分布特征及其在多金属硫化物找矿中的指示作用

热液羽状流是海底热液活动的重要标志，海底多金属硫化物是热液活动的产物。现阶段洋中脊多金属硫化物勘探工作的第一步是开展热液羽状流的近底探测；综合各类异常信息，实现从发现热液活动喷口到发现矿床的突破。本文以热液羽状流为研究对象，从羽状流的近底探测、扩散机制和分布特征3个方面，概述了最新的研究进展和有待完善的方面，阐述了羽状流在洋中脊多金属硫化物找矿中的指示作用，最后总结性地指出时空连续性、参数多元化将是热液探测的发展趋势，有助于提升对热液羽状流分布特征的认识，将为热液区分布模式的研究提供更加精细的探测资料。     

Mineralogical characteristics of polymetallic sulfides from the Deyin-1 hydrothermal field near 15°S,southern Mid-Atlantic Ridge

A seafloor hydrothermal field, named Deyin-1 later, near 15°S southern Mid-Atlantic Ridge(SMAR) was newly found during the 22 nd cruise carried out by the China Ocean Mineral Resources Research Development Association(COMRA). Sulfide samples were collected at three stations from the hydrothermal field during the26 th cruise in 2012. In this paper, mineralogical characteristics of the sulfides were analyzed with optical microscope, X-ray diffractometer, scanning electron microscope and electron microprobe to study the crystallization sequence of minerals and the process of hydrothermal mineralization. According to the difference of the ore-forming metal elements, the sulfide samples can be divided into three types:(1) the Ferich sulfide, which contains mainly pyrite and chalcopyrite;(2) the Fe-Cu-rich sulfide consisting predominantly of pyrite, chalcopyrite and isocubanite, with lesser amount of sphalerite, marmatite and pyrrhotine; and(3) the Fe-Zn-rich sulfide dominated by pyrite, sphalerite and marmatite, with variable amounts of chalcopyrite, isocubanite, pyrrhotine, marcasite, galena and gratonite. Mineral precipitations in these sulfides are in the sequence of chalcopyrite(isocubanite and possible coarse pyrite), fine pyrite,sphalerite(marmatite), galena, gratonite and then the minerals out of the dissolution. Two morphologically distinct generations(Py-I and Py-II) of pyrite are identified in each of the samples; inclusions of marmatite tend to exist in the coarse pyrite crystals(Py-I). Sphalerite in the Fe-Zn-rich sulfide is characterized by a"chalcopyrite disease" phenomenon. Mineral paragenetic relationships and a wide range of chemical compositions suggest that the environment of hydrothermal mineralization was largely changing. By comparison, the Fe-rich sulfide was formed in a relatively stable environment with a high temperature, but the conditions for the formation of the Fe-Cu-rich sulfide were variable. The Fe-Zn-rich sulfide was precipitated during the hydrothermal venting at relatively low temperature.     

TEM investigations of South Atlantic Ridge 13.2°S hydrothermal area

According to the exploration contract about polymetallic sulfides in the SWIR （Southwest Indian Ridge） signed by China with the International Seabed Authority, to delineate sulfide minerals and estimate resource quantity are urgent tasks. We independently developed our first coincident loop Transient Electromagnetic Method （TEM） device in 2010, and gained the TEM data for seafloor sulfide at South Atlantic Ridge 13.2°S in June 2011. In contrast with the widely applied CSEM （Marine controlled-source electromagnetic） method, whose goal is to explore hydrocarbons （oil/gas） of higher resistivity than seawater from 102 to 103 m below the sea floor, the TEM is for low resistivity minerals, and the target depth is from 0 to 100 m below the sea floor. Based on the development of complex sulfide geoelectrial models, this paper analyzed the TEM data obtained, proposing a new method for seafloor sulfide detection. We present the preliminary trial results, in the form of apparent resistivity sections for both half-space and full-space conditions. The results cor- respond well with the observations of the actual hydrothermal vent area, and the detection depth reached 50-100m below the bed, which verified the capability of the equipment.     

Two New Hydrothermal Fields at the Mid-Atlantic Ridge

Two new major hydrothermal fields have been discovered in the rift valley of the MAR at 13°N (Ashadze) and l6°38′N (Krasnov). The Ashadze field consists of a cluster of active hydrothermal sites associated with ultramafic rocks and located at the greatest depth in the ocean (4,200 m). By contrast, the Krasnov field consists of inactive sulfide mounds hosted in basalts. The Krasnov is the largest hydrothermal deposit on the MAR (17.4 Mt) so far discovered with iron sulfide as the principal mineral type. By contrast, Cu-Zn sulfides are the major minerals in the Ashadze deposits, which are also enriched in gold and several other metals.     

<Superscript>230</Superscript>Th/<Superscript>238</Superscript>U dating of hydrothermal sulfides from Duanqiao hydrothermal field,Southwest Indian Ridge

Duanqiao hydrothermal field is located between the Indomed and Gallieni fracture zones at the central volcano, at 50°28′E in the ultraslow-spreading Southwest Indian Ridge (SWIR). Twenty-eight subsamples from a relict chimney and massive sulfides were dated using the ²³⁰Th/²³⁸U method. Four main episodes of hydrothermal activity were determined according to the restricted results: 68.9–84.3, 43.9–48.4, 25.3–34.8, and 0.7–17.3 kyrs. Hydrothermal activity of Duanqiao probably started about 84.3 (±0.5) kyrs ago and ceased about 0.737 (±0.023) kyrs ago. The periodic character of hydrothermal activity may be related to the heat source provided by the interaction of local magmatism and tectonism. The estimated mean growth rate of the sulfide chimney is <0.02 mm/yr. This study is the first to estimate the growth rate of chimneys in the SWIR. The maximum age of the relict chimney in Duanqiao hydrothermal filed is close to that of the chimneys from Mt. Jourdanne (70 kyrs). The hydrothermal activity in Dragon Flag field is much more recent than that of Duanqiao or Mt. Jourdanne fields. The massive sulfides are younger than the sulfides from other hydrothermal fields such as Rainbow, Sonne and Ashadze-2. The preliminarily estimated reserves of sulfide ores of Duanqiao are approximately 0.5–2.9 million tons.     

Geochemistry of pyrite and chalcopyrite from an active black smoker in 49.6°E Southwest Indian Ridge

Active hydrothermal chimneys, as the product of submarine hydrothermal activity, can be used to determine the fluid evolution and formation process of potential volcanic-hosted massive sulfide deposits. A hard-won specimen from an active hydrothermal chimney was collected in the 49.6°E ultraslow-spreading Southwest Indian Ridge (SWIR) field through a television-guided grab. A geochemical study of prominent sulfide (e.g., pyrite and chalcopyrite) included in this sample was performed using laser ablation inductively coupled plasma mass spectroscopy. The early sulfides produced at low temperature are of disseminated fine-grained anhedral morphology, whereas the late ones with massive, coarse euhedral features precipitated in a high-temperature setting. The systematic variations in the contents of minor and trace elements are apparently related to the crystallization sequence, as well as to texture. Micro-disseminated anhedral sulfides rich in Pb, As, Ni, Ba, Mn, Mo, U, and V were formed during the initial chimney wall growth, whereas those rich in Sn, Se, and Co with massive, coarse euhedral morphology were formed within the late metallogenic stage. The hydrothermal fluid composition has experienced a great change during the chimney growth. Such a conclusion is consistent with that indicated by using principal component analysis, which is a powerful statistical analysis method widely used to project multidimensional datasets (e.g., element contents in different mineral phases) into a few directions. This distribution pattern points to crystallographic controls on minor and trace element uptake during chimney growth, occurring with concomitant variations in the fluid composition evolutionary history. In this pyrite-chalcopyrite-bearing active hydrothermal chimney at the SWIR, the metal concentration and precipitation of sulfides largely occurred at the seafloor as a result of mixing between the upwelling hot hydrothermal fluid and cold seawater. Over the course of mixing, significant variations in metal solubility were caused by changes in temperature, pH, and redox conditions in the parental fluid phase.     

西太平洋岛弧-弧后盆地热液活动与硫化物特征

基于国内外研究成果对西太平洋岛弧-弧后盆地热液活动的分布规律、扩张速率、水深以及热液硫化物的矿物组成与金属品位等特征进行探讨。西太平洋岛弧-弧后盆地热液硫化物区以活动型热液区为主,受扩张速率的影响明显主要分布在20～60 mm/a地区;水深分布规律主要受所处构造单元的水深特征控制,而非由热液硫化物区的形成特征所决定;研究区内的热液产物主要为富Zn-Cu、富Ba-Zn以及富Fe-Cu型硫化物;热液硫化物中冲绳海槽具有最高的Ag、Pb含量,劳海盆具有最高的Zn含量,马努斯海盆和伊豆-小笠原-马里亚纳海槽具有较高的Au含量,北斐济海盆具有最高的Cu含量。本研究将进一步为西太平洋岛弧-弧后盆地地区热液硫化物资源的勘探与潜在资源量的估算提供参考。