A 2D seismic reflection dataset of the Caosiyao giant porphyry Mo deposit in the shallow coverage area in Jining, Inner Mongolia, China

Prospecting for and exploiting buried mineral deposits is currently challenging. Given their high precision and resolution, reflection seismic methods might be useful in such applications involving deep mineral deposits. However, there are few open seismic datasets available from mineral deposit exploration, especially in hardrock environments. The world‐class Caosiyao porphyry Molybdenum deposit (1.76 Mt) in the Jining area of Inner Mongolia, China, is largely covered by loess layers, which poses challenges to its exploration. Seismic reflection surveys were conducted to help delineate the deep granite porphyry intrusions and associated orebodies. This paper presents the raw seismic reflection dataset from three profiles on the Caosiyao deposit area, which can be used as a standard dataset for reflection seismic processing in shallow coverage and hardrock areas. Situated at the juxtaposition of the Khondalite Belt and the Trans‐North China Orogen in the northern North China Craton, the Jining region hosts considerable known porphyry Mo deposits. As such, this open dataset can assist in research on deep geological structures and hence increase prospecting efficiency in geologically similar areas.


| INTRODUCTION
Mineral prospection and exploitation in areas with unconsolidated sedimentary cover is currently challenging.Although many geophysical survey methods (e.g., electrical, magnetic, gravity, seismic, remote sensing methods) exist, a general, effective, and feasible exploration technology system for use in any mineral exploration remains elusive.Among these geophysical methods, non-seismic methods, including electromagnetic, induced-polarization, and potential-field techniques, have contributed considerably to mineral exploration at shallow depths for decades (Cameron et al., 2004;Eppinger et al., 2013;Liu et al., 2021;Meng et al., 2019;Yan et al., 2021).However, because of their underlying physical principles, these non-seismic methods suffer inherent limitations with respect to their sensitivity and resolving power at deep depths.With the depletion of known shallow deposits and declining rates of new deposit discovery, seismic methods, which offer high precision and resolution as well as large detection depths, making them the most important and relied upon tool for the oil and gas exploration, also may represent a solution for the prospection of deep-seated mineral deposits (Buske et al., 2015;Eaton et al., 2003;Górszczyk et al., 2016;Lv et al., 2010).However, there are few open seismic datasets available from mineral deposit exploration, especially in hardrock environments.
The Caosiyao deposit, located at the Liangcheng uplift of Inner Mongolian massif (Axis), in the middle part of the northern margin of the NNC, is a newly discovered porphyry Mo deposit under the cover of thick loess.Geochronology studies have shown that the Caosiyao deposit was formed during the Late Jurassic (ca.150-148 Ma), which is nearly contemporaneous with the formation of the host granite porphyry (Fan et al., 2018;Nie et al., 2012Nie et al., , 2013;;Wang et al., 2017;Wu et al., 2016).The Mo mineralization primarily occurs as dissemination and stockwork in Mesozoic granitic porphyries.The ore-bearing granitoid intrusions consist of quartz porphyry, syenogranite porphyry and granite porphyry.It should be noted that the intersections of two or more groups of fractures with different orientations are often favourable for the occurrence of ore-bearing intrusive rocks and thick Mo ore bodies (Nie et al., 2012).
The areas surrounding the known Caosiyao deposit in the northern NCC also have a high potential to develop porphyry Mo deposits.However, these areas are generally overlain by thick loess layers, which complicate mineral exploration activities (Lu et al., 2022).As an important 'penetrating' detection method, the reflection seismic method has advantages in terms of achievable exploration depth and resolution that could allow it to contribute greatly to hardrock mineral exploration activities (Buske et al., 2015;Górszczyk et al., 2016;Malehmir et al., 2014).Reflection seismic surveys have been carried out by predecessors for the exploration of porphyry Mo deposits in this area and has enabled the delineation of the location of deep rock masses which accord with other geophysical measurements and inversion results (Chen et al., 2021;Xu et al., 2022).
To help overcome the lack of publicly available geophysical datasets in shallow covered areas or hardrock areas, we provide a new open dataset for the Caosiyao mining area.We then present the processing steps and analyse the seismic sections in detail, and our dataset thus provides support for better understanding the deep geological structures of the study area and delineate the location of the shallow and deep rock masses.By sharing the associated seismic dataset and its supporting datasets in the Caosiyao mining area, we provide data to support better understanding of the deep geological structures of the study area, and standard datasets for seismic reflection processing in areas with shallow coverage areas or hardrock areas.

| 2D seismic reflection exploration profiles
Three two-dimensional (2D) seismic reflection exploration profiles were completed in the Caosiyao deposit area with a total length of 20 km (8 km for the seismic profile 8, 8 km for the seismic profile 16, and 4 km for the seismic profile 3), 488 shots were stimulated by the combination of double-couple seismic sources (Figure 1c).Profiles 8 and 16 ran in an approximately east-to-west (E-W)striking direction, and profile 3 ran in an N-W direction.The nominal receiver and shot spacing were 10 and 100 m, respectively.

| Field measurements
Due to the high accuracy requirements of seismic sources and detection points in seismic acquisition, four Trimble R4 double-frequency Real-time kinematic (RTK) were used in the field.The RTK static nominal accuracy of is ± (5 mm + 1 ppm Rate Monotonic Scheduling [RMS]), and the RTK dynamic nominal accuracy is ± (10 mm + 1 ppm RMS) in the horizontal direction and ± (20 mm + 1 ppm RMS) in the vertical direction.Meanwhile, one laptop was used for interior work.
2.2.2 | Field seismic acquisition 2D land seismic reflection exploration techniques were utilized for field data acquisition.To ensure acquisition quality and exploration depth, the international advanced super detector and double controllable seismic source combined excitation instruments were adopted.A Sercel 428XL digital seismic acquisition system was used for recording, and the controllable seismic source combination of a 2013 French Nomad-65 65,000 pounds (28 tons) was used for excitation (Table 1; Table S1; Figure 2).
During seismic detection in the field, it is necessary to ensure that the two controllable seismic sources adhere to strict GPS timing and synchronization to meet the quality requirements of each shot.Given the detector's high sensitivity, the survey was postponed whenever wind, snow, automobiles activity, human movement, or other potentially detrimental situations were encountered.

| Seismic data processing methods and techniques
To meet the challenge of adapting the reflection seismic methods and tools developed for stratified sedimentary environments to strongly scattering crystalline rocks, data processing and imaging during the pre-stack and post-stack sequence required special attention to enhance the reflection signals (Wu et al., 2020).The main seismic data processing technologies used in this project are as follows.
With just a few significant reflections in the raw shot collects, the seismic data's overall signal-to-noise ratio was poor (Figure 3).Ground roll, airways, linear noise, and ambient noise were the most apparent characteristics near source-receiver offsets, substantially masking important signals.Pre-stack and post-stack sequences are frequently used in the seismic reflection data processing since they have been shown to be successful in the past seismic reflection surveys in crystalline environments (Heinonen et al., 2013;Malehmir & Bellefleur, 2010;Milkereit et al., 1996).
2.3.1 | Pre-stack signal enhancement During the pre-stack stage, the primary goal is to improve signal-to-noise level by removing or suppressing noise.
1.During trace editing, bad and noisy traces with constant amplitudes and frequencies through time were first eliminated.2. Since the poor quality of first arrivals in the raw shot gathers, they were then picked automatically, inspected, and corrected manually.3. Refraction and elevation statics were corrected to remove the effects of surface elevation variations and near surface heterogeneity after the first arrivals in the raw shot gathers were picked from the entire dataset.4. Band-pass frequency and surface-consistent deconvolution filters were designed and applied to attenuate possible noise from linear coherent noise, ground roll, and air blasts to improve the overall signal-to-noise ratio.5. Amplitude compensation for seismic data was applied to amplify weak events at deep depths.6.A surface-consistent spiking deconvolution algorithm was applied to attenuate multiples and to compensate for the effects of variable coupling conditions of different sources and receivers.7. Velocity analysis and residual statics correction were combined to correct any remaining time shifts to improve the stack effect of existing reflections.
1.A common midpoint (CMP) stack was applied to stack normal moveout-corrected traces caused by the effects of source-receiver separation from reflection records.2. Dip-moveout (DMO) corrections using the background velocity interval were applied to stack reflections with conflicting dips, as reflectors in crystalline environments are prone to variations in dips (Deregowski, 1986).

Several post-stack migration algorithms including
Stolt, phase-shift, and finite-difference were tested and utilized to reposition dipping reflection events and further improve the resolution of the seismic sections.

| Seismic data quality
Shot 66, with length 6 s, was randomly selected for display, including the original wave, filtered by (14, 20-80, 86) Hz, 10-20 Hz, 20-40 Hz, 30-60 Hz, 40-80 Hz.As shown in shot gathers from Figures S1-S6, clear first arrivals and several continuous and prominent reflections can be identified.Each shot's data were analysed quantitatively (Figure 4).The results show that the basic frequency is 25 Hz, and the frequency band is between 9 and 53 Hz.The signal-to-noise ratio of single shot record (signal frequency range 20-80 Hz) is about 2:1.

| Seismic profile data
As shown in the seismic profile 8 (Figure 5), a highreflective layer with good continuity in the near-surface can be identified, which is interpreted to be the boundary between the Quaternary sediments and lower basement.According to the structure of seismic reflections, the basement under the Quaternary cover can clearly divided into western and eastern parts.The subsurface reflections in the west are comparatively shorter and weaker than in the eastern part, and only some intermittent, small-scale reflection layers are apparent.There are obvious dislocations of the axis of seismic reflection near the surface, indicating that the formation is relatively curved, and medium and small-scale fractures and folds are also abundant.Near the middle of the exploration line, where the reflection axis is significantly shifted, a large-scale fault (fracture zone) likely exists, reflecting the significant geological tectonic activity in this region.
The eastern part of seismic Profile 8 exhibits good stratification, but with poor continuity, showing multiple discontinuous distributions with multiple dislocations of the seismic reflection axis.
The reflection characteristics of deep rock layers are not obvious, which may be caused by a slight anisotropy difference of deep metamorphic rocks.
The seismic phase characteristics of the profile 16 are basically the same as those of the profile 8 (Figure S7).The closure difference between the seismic reflection exploration profile 3 and the other two is small (Figure S8).

| Seismic profile interpretation
Seismic interpretation requires not only the identification of the geometries and patterns of seismic reflections beneath, but also incorporates other geophysical, geological, logging, and other data for comprehensive judgement.
For mineral exploration applications, it is crucial to identify ore-controlling structures such as fractures, folds, and intrusions in seismic sections.The first step is to correlate the geological horizons and/or structures, where information already exists or can be inferred from other source data, with the seismic sections and identify these geological interfaces.Second, interpretated interfaces are extrapolated into unknown surrounding areas using knowledge of the reflection characteristics of various typical geological interfaces.Finally, as an increasing number of events or reflections are identified, correlated, and referenced, the spatial variability of geological features can be summarized and presented as a final structural map.
The following takes the seismic profile 8 in the Caosiyao deposit as an example of such structural interpretation.

| Structural characteristics
A series of equidistant, subparallel north-west (NW)trending faults, which were interpreted to be the Datong-Shangyi faults, were identified in the Caosiyao mining area.The concealed granite porphyry intrusions beneath are inferred to be distributed equidistantly along the Datong-Shangyi faults.Corresponding to the location of the buried fault (zone) on the geological map (Figure 1c), the existence of this buried fault (zone) is verified to extend down to high depths with a varying dip angle along Profile 8 (Figure 1d).The dip angle of the Datong-Shangyi faults at depths between 2.5 and 3.5 s is relatively low, reflecting the likelihood that the early nappe structure deformation was not very strong and that the period in which this occurred may have lasted longer.However, the shallow parts (0-2.5 s) of the faults are steeper than the deep part, indicating that the late tectonic movement was stronger than the early stage.The Datong-Shangyi structures dip from west (north) to east (south), indicating a pushover from north-west to south-east.Moreover, the multiple folds of different scales that can be seen in the shallow and deep parts, especially the multiple small folds near the surface, reflect the tectonic movement at that time.

| Physical characteristics
Since that there are many drillings in the study region (Figure 1d), it is vital to provide the densities and velocities of various rocks in order to help readers to estimate the application of the seismic method.The density parameter of regional strata is shown in Table S2, and the density of rocks and ores in Caosiyao area are shown in Table S3.The strata in the study area basically follow the overall change law of increasing density with age.The density of granite is lower than that of surrounding rocks in Jining Group.The density of molybdenite mineralization rocks is generally higher than that of the original rocks, and similar to that of the surrounding rocks of the Jining Group.
Due to the lack of sonic velocity restrictions from drilling logs in the Caosiyao deposit area, time-to-depth conversion was performed using a constant velocity of 6000 m/s, which is typical of all except the uppermost section (above 1 s) of the low-velocity sedimentary cover (about 2000 m/s) (Keaton, 2009;Tian et al., 2014).
In order to calculation the magnetic anomaly, the author provide the magnetic parameters of regional strata in Table S2, and magnetic parameters of rocks and ores in the working area in Table S3.The law of regional formation magnetic susceptibility and remanence is not obvious.The magnetic properties of granites in the Caosiyao mining area are generally low, but the molybdenite mineralized granites tend to increase.The high magnetic properties of the diabase in the area are the main factors causing the high magnetic anomalies.In addition, the total field anomaly data were converted to the reductionto-the-pole using a magnetic inclination angle of 60° and a declination of −6°.

| Orebody characteristics
As shown in Figure 6, the lower part of the contact line (ore body center) is near the center of the Caosiyao Mo ore body.However, the boundary of the concealed subsurface ore body cannot be clearly delineated in the seismic section.This is mainly because of the limited impedance difference between the ore body and the surrounding metamorphic rocks.Some intermittent small-scale layered reflection interfaces in the ore body area, which may  correspond to large faults or cracks in the magmatic rocks, are identifiable, however.
As a team work, 2D seismic reflection, geophysical methods, geochemical methods, remote sensing methods were used to carry out geological exploration of the Caosiyao mining area.The detail geophysical analysis was published by Chen et al. (2021).The 3D shear velocity structures indicated that the resolution within the Caosiyao ore deposit zone is generally adequate down to roughly 3 km.Meanwhile, the 3D shear velocity model shows that when the depths greater than 800 m, the area of high velocities that is indicative of gneiss basement and granite plutons is significantly expanded.Low S-wave velocities are characteristic of the ore body zone in the Caosiyao region, and underneath this zone, at a depth of around 800 m, is a strong shear velocity anomaly that denotes the concealed granitic pluton that drove the mineralization fluids and sources.Chen et al. (2021) used ambient noise tomography (ANT) to identified most of the faults which are located at the gradient zone of the Bouguer gravity field.ANT can more accurately define the ore deposition location with highly fractured structures and the development of water, clay, and mineralization.According to the rock density inversion, there present a small low-density zone in the deeper part and two tiny low-density zones in the eastern shallow part of the Caosiyao deposit area, which indicated several faults might exists between the two zones (Figure 6).Which is accordance with findings of high shear velocities from ANT.
2.6.4 | Inferred magma channel and source The magma that formed the ore body at the shallow depth may have intruded along the faults from west to east or from some small fractures intersecting these faults.The ore-forming magma was likely driven up forwards to form a small magma chamber, which may have gradually cooled and deposited to form the Mo ore body.On the seismic profile 8, 16 and 3, multiple faults intersecting the ore body or passing near the ore body can be observed, which may act as the tunnels that delivered magma from the deep source.
Geological transverse-section along the seismic profile 8 exploration of the Caosiyao deposit, showing types and zoning of wall-rock alteration (modified after No. 2 Geoexploration Party, Henan Bureau of Geoexploration and Mineral Development, 2014).

| DATA ACCESS
To better carry out mineral exploration and development in the study area, the need to summarize and share various exploration data for mutual discussion and verification has emerged.To address these issues, the datasets generated are shared openly via Zenodo.The data can be accessed at: 10.5281/zenodo.7322156,which are available as a password-protected (CUGofB221116) ZIP files.This identifies a seismic profile dataset that is mentioned in this paper.Briefly, the files consist of 488 shots in Caosiyao deposit area: 'Caosiyao -seismic profile 3' contains 88 single shot records; 'Caosiyao -seismic profile 8' and 'Caosiyao -seismic profile 16' both contains 200 single shot records.
The DOI can be directly incorporated into a URL using a resolver (https://doi.org)that supports HTTPS, or it can be searched for using the DataCite website's search page.For the seismic dataset, Zenodo, automatically generates a landing page which URL is associated with the relative DOI.All information about the requested data can be immediately seen in this page (Figures 7).From here it is possible to download directly the data.

POTENTIAL
Although seismic reflection has a large detection depth and high vertical resolution, on account of the data acquisition costs associated with the technique, at present, the detection of ore bodies is still dominated by 2D profile detection.Large-scale three-dimensional (3D) area detection is rarely carried out.Therefore, the obtained results are mainly to establish the "skeleton" structure of the ore bodies.When the lateral structure of the study area changes sharply and/or the geological structure is complex, the limited seismic profiles cannot capture the entire regional structure.
In addition, on account of the cost and low coverage of 2D seismic reflection techniques, less seismic data than other types of geophysical data are currently obtained.For researchers using other exploration techniques and methods in this area, seismic data can act as a useful auxiliary constraint to better identify the deep structures of the Jining region and to lay a solid foundation for the further exploration.

| CONCLUSIONS
Single shot seismic reflection data from the Caosiyao deposit area were collated and processed to form three highprecision 2D seismic profiles with a total length of 20 km.These stacked and processed seismic sections contain several clear and strong reflectors, indicating that the quality of the acquired seismic data is relatively high.understanding of the study area's subsurface structural characteristics was obtained, including the delineation of the location of the shallow and deep rock masses.
Finally, sharing the seismic dataset of the Caosiyao deposit provides evidence for the deep geological structures in this area as well as an example dataset for reflection seismic processing in areas with shallow coverage or hardrock.
In accordance with the FAIR Principles, the entire dataset is made accessible for download via Zenodo.

F
I G U R E 2 Schematic diagram of controllable source seismic exploration in hard rock areas.F I G U R E 3The original data of shot 66 from the seismic profile 16.

F
I G U R E 5 The time-migrated stacked seismic profile 8 in Caosiyao survey area.

F
Comprehensive Interpretation of Seismic Profile of Line 8 in Caosiyao deposit area.
with the tectonic background, geological map, and related gravity, 2D seismic reflection, and other geophysical data from the study area, a comprehensive geological interpretation of the superimposed migration sections of three 2D seismic profiles in Caosiyao could be conducted.From this, a more comprehensive F I G U R E 7 Preview of the Seismic dataset of Caosiyao deposit after DOI resolution.
Seismic equipment and engineering accessories for the Caosiyao seismic survey.
T A B L E 1