Overview
Jade Quarry is a fun, wide-open competitive mission located south of Cavalon and far east of House Zu Heltzer, at the very NE corner of Melandru's Hope. It does not have the same straightforward gameplay as the Fort Aspenwood mission and resembles Alliance Battles more closely. Due to the lack of natural "herding" barriers like the narrow gateways present in Fort Aspenwood, the Jade Quarry plays and feels more like a giant bowl, which can disorient new players unfamiliar with mission objectives.
Gameplay
The main objective of the mission is to ensure that your team holds as many of the three quarries as possible, so that the carriers - Kurzick Juggernauts and Luxon Turtles - can carry blocks of jade back to your base. As soon as the block is crushed under the mechanism your team will score a point. The team that scores ten points first, or the team that scores the most points when time runs out, wins.
The main gameplay objective, then, is to capture and recapture the quarries as frequently as possible. Initially, in order to capture the quarry for your team you must enter it before the enemy does. This will spawn your team's NPCs inside the quarry, as well as start a carrier. Once the NPCs spawn, capturing a quarry requires killing all of them, which can be quite problematic to achieve in one attempt, especially if you're also being harrassed by the other team.
Most inexperienced teams put too much emphasis on killing players or capturing guard posts, and while both strategies net faction points and XP neither does as much for your team as capturing a quarry. The Longbows that spawn at each guard post can slow down enemy players and carriers with Pin Down, but they generally constitute an annoyance rather than a threat and can be avoided easily. Likewise, killed players quickly resurrect at the base with full energy and can get back into the battle with minimal downtime due to the teleporters.
Location is the main thing to remember while playing in the Jade Quarry. Frequently it is better to capture a quarry and die than run or fight simply because you will come back with full energy at your base and can reposition yourself, moving out through a teleporter to any quarry that is left unguarded or requires recapturing. You can spend less time dying to three Longbows, coming back at the base and teleporting to the other side of the map than you will running over - which is a dangerous proposition even with a running skill.
Another thing to remember is to always use the "U" window while playing in competitve maps with multiple map markers. You don't have to keep it open all the time so it doesn't obscure your vision, but checking the minimap every once in a while will let you know which quarries and guard posts your team holds and which ones you should be focusing offensively on. Checking the minimap while waiting for resurrection is perfect because you can then teleport to the appropriate location rapidly.
Tactics
Jade Quarry is a nuker's paradise. Guard post and quarry NPCs are bunched up tightly in their starting locations, and nothing kills them faster than a properly placed AoE fire magic spell. That said, there is something to do in Jade Quarry for everyone.
-Warriors are the main harrassment machines in Jade Quarry. The best setup for a warrior is not to damage and kill NPCs but to distract them while a caster kills them, and to eliminate enemy players who might try to recapture the quarries. Speed buffs are essential for chasing down enemy casters, as are protective skills that will allow you to survive the attacks of NPCs while you hold their aggro. Distracting Blow is perfect for interrupting key enemy skills, and you want to bring condition and hex removal to prevent yourself from being killed too easily. Unlike the casters who can quickly resurrect with a new supply of energy, you are most useful while you're alive and in the face of enemy casters. Cyclone Axe and Triple Chop are both valid choices if you want to set up for NPC killing instead.
-Rangers are useful as caster and carrier killers. The degeneration from poison (and bleeding from Hunter's Shot, which always works because the carriers are always moving) can take down a carrier pretty fast, and the various ranger interrupts can likewise shut down an enemy caster. A speed buff and a defensive stance will allow you to survive longer, while Barrage can help your team capture guard posts and quarries. Trapping the quarries is also a valid option, but there's no guarantee the traps will get set off by an enemy tank instead of all the enemy NPCs once they spawn. Edge of Extinction, which generally rules Fort Aspenwood if used properly, does not do as much in the Jade Quarry simply because you don't want to kill all the NPCs - including the friendly ones holding a quarry for you - at once. You don't have "disposable" NPCs like the Luxon Warriors in Fort Aspenwood to set it off, so be very careful where and when you place it if you choose to bring it.
-Assassins make excellent caster and carrier killers. Bleeding, poison and deep wound all make short work of the carriers, and speed buffs and debuffs let you catch up to carriers and players alike. You are nowhere as durable as a warrior or a ranger, though, so consider either going for hit-and-run tactics (the usual for good assassins) or run-and-die tactics (the usual for Jade Quarry casters to recover energy). If you've assassinated your target but don't have the energy or the speed buff to relocate yourself quickly, dying is probably the best option for you. Twisting Fangs and Shadow Form are two skills you should pay particular attention to, the first for killing and the second for holding NPC aggro or general invulnerability, as well as the near-instant death afterwards (unless you set up to avoid it).
-Elementalists are the main damage machines of Jade Quarry. Properly placed fire spells can eliminate guard posts in about ten seconds, while quarries generally take longer. Of the three other elemental lines only water magic offers comparable AoE damage, but the slower recharge and lack of repeated AoE damage make fire magic a clear winner. Of course, slowing down enemy players can be very helpful in the Jade Quarry, but that's not what you as an elementalist should be focusing on. Earth magic is nice too, but slow recharge and the fact that most of earth AoE is proximity based are both prohibitive. I highly recommend using fire magic skills with a three-second or shorter activation time, especially Searing/Teinai's Heat and Breath of Fire. Coupled with a Fireball or a Meteor, both of these can take out a guard post in one go. Resurrection does not remove skill recharge, so while Meteor Shower is as good in the Jade Quarry as ever you should avoid it.
-Necromancers can be nearly as good or better than elementalists in the Jade Quarry in terms of damage output, depending on the setup and the situation. While normally Minion Masters (MMs) rule any area with as large a number of corpses as Jade Quarry, the very size of the map prohibits MMs from being useful all over. Further, MMs lose control of the minions if they die, so the best thing a MM can do is help capture one single quarry and hold it with the minions to stop enemy attempts to recapture it. But Jade Quarry is a much more offense-driven map, so most necromancers set up with curses, for AoE degen and Spiteful Spirit for rapid NPC kills.
-Mesmers don't generally have a role in the Jade Quarry outside of caster distraction. As in all PvP, mesmers are excellent at shutting down enemy casters with Diversion and Backfire and interrupts, but lack the offensive capabilities to take down NPCs on their own. Since casters die and come back so frequently in the Jade Quarry a mesmer should focus not on energy denial (all energy is recovered when a character resurrects) but on things that resurrection does not remove, like exhaustion (Arcane Languor) and skill recharge (Diversion).
-Monks aren't generally as welcome in the Jade Quarry as they are in Fort Aspenwood. Healing does not play that great of a role in Jade Quarry since there are very few "safe" places from which a monk can keep NPCs alive, and since there are so many NPCs around a monk simply cannot heal them all. A smiting monk, however, would do an excellent job of capturing a quarry or guard post when paired with a tank, and could take advantage of the rapid deaths to recover energy.
-Ritualists lack the firepower to bring down the NPCs on their own, but can do well spamming spirits to protect a quarry. The spirits serve as an additional speed bump on the way of the enemy team and allow more players to converge on the quarry to defend or retake it. A channeling ritualist could try to "smite" off of a tank with Ancestor's Rage or "nuke" with Spirit Rift, but won't be able to kill as fast as most of the other offensive casters.
Strategy
The main thing to remember while playing Jade Quarry is that you're supposed to capture quarries. You should always check to see which quarries your team holds and adjust accordingly, heading to the enemy-held quarries to capture them or destroy their carriers. Jade Quarry is an offense-driven map because there are simply too many points to defend and the points are so far apart. Just as in alliance battles, it may be more beneficial to go around a defending team and capture things they aren't guarding than to confront the team head-on.
Immediately after loading, at least one nuker on your team should go to the extreme left of your starting area. There will be a guard post controlled by the enemy reachable from that spot, and you should capture it before the timer starts and the gates open so you have less work to do afterwards.
Split your team into two roughly equal groups and head towards the side quarries on the east and west walls of the battle area. If you are Kurzick, send a runner to capture the south quarry since it's located closer to you. If you are Luxon, consider sending a nuker and another character to the south quarry to put pressure on it right away while the rest of the teams are engaged elsewhere.
While heading out to quarries, do not use the main gate! Teleporters generally deposit characters closer to quarries than gates do, and even if you have a speed buff you can always activate the speed buff after teleporting. The teleporters are also much closer to the resurrection point than gates are.
If you succeed in capturing a side quarry, push on into enemy territory. If you encounter no resistance, capturing a guard post will provide a speed bump to the enemy's attempts to recover the quarry. If you meet resistance and die, refocus the attack on another quarry: while your enemy will be killing your NPCs you will have a chance to kill theirs and get an extra carrier. After that, you can come back to the original quarry and recapture it, since your enemy will likely have moved on.
Your team only needs to hold two out of the three quarries to win in the long run, but remember that your enemy will not be sitting on their hands and just let you win (if they've read this guide

Killing a carrier is not as good as capturing a quarry in that it does not let your team score, but it does prevent the enemy from scoring. If you're set up to kill enemy carriers, try to hang out somewhere near the central intersection of the map. All carriers must travel over level terrain, so - for example - Kurzick Juggernauts from the east (green) and south (purple) quarries must go through the intersection SE of the two guard posts and the jade outcropping. If you're going to take on any guard posts, try to capture those two because they overlook the main avenues of carrier advance to their respective bases. Pin Down can let you have a little bit more time to kill those pesky carriers.
And lastly, if you're only coming to Jade Quarry in order to unlock your map, participate first and map second. "Mapping leavers" give a bad name to all cartographers and are currently part of the reason Jade Quarry sees little to no action.
Afterword
I know that Jade Quarry is mostly a ghost town, but it's an incredibly fun mission to play. It gets more populated in the evenings and on the weekends, and I believe that if people actually knew how to win in it things would change and it would see a population increase. So instead of mapping and leaving, or just asking Fort Aspenwood people to move over, do your part. Don't be a part of the problem; be a part of the solution. Walk your guildmates to Jade Quarry today, and tomorrow there might actually be enough people there for everyone to get in!